Java Basics

1JDKJava Development KitJDK = Compiler + JVM + JRE > Java Virtual Machine, Java Runtime Environment.Compiler compiles source code to Byte code, JVM execute Byte code and convert it to Binary code. JVM responsible for running Java application. JRE is a collection of tools that run Java application.Jdk is owned by Oracle, Stable version is 8, can use 11.Open Jdk is like corretto 1.8, some Third Party organization like amazon who derived their Jdk from Oracle version and further support and maintained it. For Example : JDK Corretto 1.8 is useful to run uiautomatorviewerCore Java vs Java Standard Edition > Core Java is the standard edition from which other editions are derived, So both are same.Install Jdk
2Computer Architecture LanguagesHigh Level LanguageHuman UnderstandableIs more english like language
Low Level LanguageM/c UnderstandableIs a language in binary numbers
3Java Files.java file in which High level code writtencompiled by compiler to .class file which have byte codeclass loader is Java internal API which upload .class file to JVM (Java virtual Machine), JVM on the target machine will convert this byte code to machine understandable binary code and executes it.JVM then pass on instructions to Interpreter for Mac, Windows or Linux which then show result on output console. Interpreter is from OS side
.class file created in same folder if created by terminal or 
.class file created in bin folder if created by eclipse
In Eclipse, .class file can be seen by Navigator view under Window Menu which is deprecadted now
4Mavenonline repository for dependenciesDownload jar files automatically in ProjectDownload and unzip it in any folder. Stable version 3.6.3
5Environment VariablesSystem Variables are available to all Users. It is at OS Levelare in the form of KEY and VALUE pair.“Path =” This key already defined in OS (in-built variable) and value given against this key is understood by OS > executables or batch files values given against this keySuch as here for Java, path is to given upto bin folder where all executables files are presentJAVA & JAVA_HOME are two different variables
3rd Party varaibles are available to all Users. It is at OS Level3rd Party variables are set to make connections between system softwares & applicationsThird Party Variabales are like “JAVA_HOME “. These variables name are standard and can be used by third party applications or other applications installed in the OSSuch as here for JAVA_HOME, path is to given upto jdk folder where all files are presentSet MAVEN_HOME too by path upto Maven Folder/bin on Hard Disk
User varaibles are avaible specifically for that user who is logged in
6Integrated Development Environment (IDE)Code Editor Which integrates with JDK + Maven + OthersEclipse >Download from packages and unzip it: Eclipse IDE for Java Developers
Set Jdk path in Eclipse >Eclipse > Window > Preferences > Java > Installed JRE > Add > Std JVM > Select jdk folder from SSD > finish
Java library > contains all jar files of JRE frameworkrt.jar >Its contains all compiled class files for the Core java and bootstrap classes which required during runtime. These classes comprise of Java platform Core API
Java perspective (Right icon with J letter) & Open Perspective icons at top right corner of EclipseThis means nature of Eclipse to be to associate with projectsDefault is Java perspective
Console view in eclipse is like terminal in Mac OS Shows us the output while executing Program
Add/Choose specific Jdk for Specific project >Project Folder > R.click > Properties > Java build Path > Libraries Tab > JRE Library > Add Library > Select Jdk > Apply and close
Shorcuts >To type main method in Java class is : main (ctrl+space)Ctrl + S > saves and compiles the file
CODING :-
7LogicLogic is the working principle on which software built (What, Why & How). It is also called Business Logic.It is contained in the set of instructions written by programmer.
8ObjectSimply its entity having knowledge of something of specific point of time which may or may not update according to set conditionsMore Clarity: Its copy of class at given point of timeObject can be Value, Variable, Data Structure, Method, Table or combination of these. It also defines the Instance of class in class based OOPS
9Object Oriented Programming Structure (OOPS)Object called to get or set the valueIs the type of computer programming where programmer is using the idea of object for defines the data type of data structure and also defines the type of fx’s that can applied to data structure. Simply means which data to get or set by the use of object
10KeywordReserved words whose meaning already defined to compiler
11TemplateIt is a file which is pre-formated in some way and serves as a starting point for new document
12InstanceIs also called StateConcrete Occurance of Object
13InheritanceIs a mechanism where which one object/class acquires all the properties and behaviors of a parent object/classCan access the member of inherited class into inheritance class
14Name SpaceMeans Group, Collection of classes, It may be nested
15Data StructureIt is the data organization, management & storage format, that enables efficeint access and modifcation.It Is the collection of data values and relationship amoung them
16StringIt is sequence of characters stores in character array and marks in double quotation marks ” “
17ArrayCharacter array is collection of variables of char data type and stores in consecutive memory addresses
18ConcadinateJoining two texts together in one cell from two different cells
19PointersIs a variable that store address of memory location
20Create a Java ProjectNew – Java Projectsrc folderpackageclassmain methodrun as Java application
21Create a Maven ProjectNew – Maven Projectsrc/main/java & src/test/java folderpackageclassmain method & pom.xml file or Convert to TestNg execution approach which creates testng.xmlrun as Junit / TestNg Test
22ClassClass is defining idea in OOPSIt is template definition of methods & variables or it can be a particular kind of object. It is also collection of similar data types.Used for re-usability, Also Called Business Objectpublic class name {  }
Instance Properties >Block{  }Execute before to Methods and runs every time as the objects created{ } constructor(); method(); Methods run after constructor and Constructor run after Instance blockstatic block Loads first along with the class and execute once only even if many objects created during execution. It runs before to instance block
These are the properties of the class and declared directly within class and have scope everywhere in the class but are always used with object.VariableIt is the entity that changed, It use to store & retrieve data from memory locationJust inside the Class Curly Brackets & Declare (Just create) or Initailize (provide first value) there.public class name { int A = 100;  }; called statement terminator
MethodDefines the behaviour of object, it is the action that object can able to perform. Methods required an object of its class to be created before it can be called.Inside class curly Brackets public void methodOne() {};
A method is a block of code which only runs when it is called. Methods are used to perform certain actions, and they are also known as functions.Method start with return type either primitive, non-primitive or voidname() { } with or w/o argumentspublic static void main(String args[]) { } :- main method in Java :-
>> same name methods can be use but number of arguments or sequence of arguments must be differentvoid is also the return type as it will return nothingIf Return type is of Primitive data types then method returns value and If Return type is of non-Primitive data types then method returns objectmain method is entry point in java and excution of java program starts from this method, all other methods called in this method
Local Properties >If any above property used inside Method it is called Local Property to that MethodThey have scope from their point of initialization to the end of block in a class. i.e. end of methodLocal variables have no default value and they must be initialized (or have some value) before being used otherwise there is compile-time error.
Static Properties >Any property used at Instance Level can be static, static not use with local propertyIf we use Keyword Static then its means we call method without creating objectStatic property Called with class name or directly But normal property always called with objectnon static method/property can be called from static method with the help of object And static method can called static property directly.  from inside static method, non static method can be called in same class with the object of class like object.nonStaticMethod(); AND static method can call static method directly or with class name. 
Static means no duplicacy, only one instance of thing which once updated then always keep its updated valuestatic block at instance level executes onece only but normal block at instance level execute all time when ever class constructor runStatic method can call static variable or static method directly, static method can call non static constructor as static keyword Not Applicable to constructornon static method called static method with the class name like ClassName.static Method
23Naming Convention (Camel Case)Variable Name =>start with small letter + Camel Case >startName = 1;
Method Name =>start with small letter + Camel Case >startName() { };
Class Name =>start with first Capital letter + Camel Case >StartName { }
Project Name =>start with first Capital letter + Camel Case >StartName
final Variable Name =>all Capital Leters + can use _ >final START_NAME = 1;
Packages Name =>Domain_Name.Application_Name.Module_Name >com.neimanmarcus.kids >Package can be of 2 types, like inbuilt package & user defined package >1) One class called into other class in same package then not need to import and need to import if called from other packageimport com.package.*; > This call all classes under this package
Interface Name =>start with small letter + Camel Case >startName();2) class can be called also as package_Name.class_Name object = new package_Name.Class_Name(); This is called fully qualified class name
24Data TypesCapacity: byte = 8 Bits = 1Byte => Range of Values: Signed: -128 to 127 OR Unsigned: 0-255<<— Primitive Data types –>These are basic data types and their value directly stored in memory like Byte, short, int etc and from these other data types can be derived >like String is derived data type
short = 16 Bits = 2Bytes => -32768  to 32767Primitive int variable has default value of 0.
int = 32 Bits = 4Bytes =>[ -2147483648 (2^31)  to 2147483647 (2^31-1) ]Primitive boolean data type has default value “false”.
long = 64 bits = 8bytes =>-9223372036854775808(-2^63) to 9223372036854775807(2^63 -1)Primitive char variable has default value – nothing.
float = 32 Bits = 4Bytes =>[ -3.40E+38 (3.4 * 10 raise to power 38) to 3.40E+38 ]it is mandatory to write f or F with float value like float abc = 54.66f;
double = 64 bits = 8Bytes =>[ -1.7e+308 (1.7 * 10 raise to power 308) to 1.7e+308 ]no need to write f or F with double value like double abc = 54.66465747;
char = 8 Bits = 1Byte =>take any characters out of these from 0-127 => ‘a’-‘z’ or ‘A’-‘Z’  ‘&’, ‘@’, ‘0’-‘9’ AND Other symbols
boolean = 1 bit => true or false = 0 or 1
bit = 0 or 1Signed means it contains negative & positive values AND unsigned means it start from zeroNon – Primitive Data type —>>is a class and can be access by objectString is non-primitive data type and it is the class defined in Java and its take set of characters/integers or symbols written under double quotesString store as object
User defined classes are also as Non – primitive data types and have non – primitive variables which are accessible thru objectAddition obj; > Addition here class name and obj is its object name, Can have multiple data types in itArray List eee; > Can have rows only, Can have rows & colums, Can have Key : Value pair, Is of one data type
Non-Primitive instance variable has default value null.Null is a Object in Java with no size and no dimensions
Local variables have no default value and they must be
initialized before being used otherwise there is compile-
time error.
Reference Variables –>>Refers to memory location which stores data Like Null Object and thus value assigned to null object after execution of code
25Type casting for DataAre of two types :- implicit (means happened automatically) & explicit (means need to do intentionaly)implicit is also called widening like byte to short > int > long > float > doublethis convertion happened automatically like short + byte = int by default in java or int + double = double
explicit is also called narrowing like double to float > long > int > short > bytethis need to do intennationally by type cast like int = (int) (long + double)
26Access Modifierspublicprivateprotectedif no modifier given => it is also called default modifier but no keyword to write thereThese can be applied to class, variable, method, block & Constructor
scope/available thru out in same classavailable thru out in same classavailable thru out in same classavailable thru out in same class
available to other class in same packagenot available to other class in same packageavailable to other class in same packageavailable to other class in same package
available to other class in different packagenot available to other class in different packageavailable to other class only if this first class is sub class of Called class which means “extends” as Parent – Child relation. Variable from Parent class called with object of current class which created wih new keywordnot available to other class in different package even if “extends”
Not available in other projectNot available in other projectNot available in other projectNot available in other project
protected methods and variables work with keyword “this” as (current class) object and not with “new” object of extends class ?
27Creation of ObjectObject is something which occupies memory, has size and dimensionsWhen object created, whatever is with class at that time, comes to that object > Simple Means copy of class created which have all the Instance propertiesObject can be initialised by Puppy1 pup1; or Puppy1 pup1 = null; Here Puppy1 is the classalso use to create object => packageName.constructor();
Box obj = new Box(); :-Box >Is the class name >Its load the class in JVM and also load the static variables and static methods and final variables, final methodsstatic variables and static methods can be access without object of classs & with the class name
obj >is the object name >Object is used to access instance variables and instance methods
new >is the keyword >New memory allocated and After this keyword, instance variables and instance methods loads in JVMnew keyword also execute instance object created in that class with new keyword and execute constructor which associated with it
Box() >is the constructor of class >after this, object creation completed
28Class Constructor1)Constructors are not Properties of class but variable and methods are.Constructor is like method with class name and have no return type
2)are used to create object
3)Puppy = Puppy();Left side Puppy is class name and right side is that class constructor
4)have no return type
5)constructor can be multiple and can be overloaded inside classOverloading means : Same name with in same class but arguments or sequence of arguments can be differ
6)If argument pass on to constructor then it is called Parameterized constructorIf no argument pass then it is called default constructordefault constructor can only be created automatically in class if no any parameterized constructor present so farIf to use default and parametrised constrcutor, then both need to present in class
7)Constructor can be used to initialize instance variable without calling method>int x ; > Puppy(100);One class constructor called from other class without extending the first class
29“this” Keyword“this” : it is a object and called as calling object and defined as current class – current object It called implicitly, means automatically. If any instance object or varaible is called (at class level)) then this keyword add automatically.If same name varaible or object is present in current method and to call instance object then this keyword to use like :-this.name = name :-By this statement, local variable assigned to instance variable by using keyword this
It is not used where static keyword is in useinstance object called when this keyword used or when same name object is not present in current method then “this” keyword fixed automaticlaly but it is in hidden stateclass example { float dd = 50.54; void abc() { float dd = 100.11; System.out.println(this.dd);  System.out.println(dd);}
local object called with in current method only without keyword thisThis print 50.54 as instance variable called with keyword “this” and 2nd ans id 100.11instance object called when this keyword used or when same name object is not present in current method then “this” keyword fixed automaticlaly but it is in hidden statelocal object called with in current method only without keyword ‘this’
30“final” keywordThis keyword is used where to provide value for variable which would not be change at any stageIt can be use before class, method or variableIf final used then value must be given for that variable.
final means constant valuefinal variable cant be changefinal method cant be overridefinal class cant be extend and cannot extend other classes
31Null Pointer ExceptionIt is caused when Object refrence is null and trying to access its properties >class Addition1 { int x = 100; Addition1 add = null; System.out.println(add.x);}If the object is null even then its know about all the static properties of class of which that object is. So it can show result for static properties
null have no size, no dimension, no memory but points to memory locationPrinting of x here gives null pointer exception as object “add” have null reference however x was defined. x when merged with any object then it should not be null to avoid NPE.
32Escape SequenceSystem.out.println(x + ” \” ” + name) >here \ called as Escape Sequence which means just ignore itself & ignore next character as a code and take it as a String Object – one of member in String value10 ” Kamalthese only charters to use after back slash : \b, \t, \n, \f, \r, \”, \’, \\
System.out.println(x + ” \” amit \” ” + name) >10 ” amit ” Kamal
System.out.println(x + ” \\” amit \” ” + name) >10 \” amit ” Kamal
“\n abc “Print abc in new line“\r abc “Print abc in next row
” \t abcPrint abc after one tab space
” \b abcPrint abc with one back space
33Prement Incrementx = 5 > plus plus x (++x) > This means 1+x = 6 & the value of x this time update as 6 as increment predone to original xint ab = ++x;
System.out.println(ab);
System.out.println(x);
Post Incrementx = 5 > x plus plus (x++) >This means x+1 = 6 but the value of x this time remains as 5 as increment done after running this codeint y = 5;

int z = y++;
System.out.println(z);
System.out.println(y);		//this statement increases the value of y by 1 
//but will use its current value this time 
//and next time when you will use y, you will get its incremented value.
34two == or .equals Operatortwo == check the memory location or compare memory location .equals compare content or value.equals operator is not applicable to Primitiave Data type
abc == xyz variables should have same value then returns boolean true but both objects should made by String Literal Methodabc.eqauls(xyz); should have same value then returns boolean true whether the objects made by String Literal or String Object Method by ‘new’ KeywordEquality can be check for same data type
Called Object equalityCalled Content Equality
354 Pillars of JAVA# Polymorphism >Same name but arguments are differents or sequence is diff. called overloadingSame name and same argument but in other class called overriding
# Encapsulation >variables are private and assigned values by public setter or getter methods 
# Inheritance >aquiring properties of parent class with extends KeywordUpcasting & Class Casting is also related to it 
# Abstraction >Body for method provide in child class 
36PolymorphismPoly means many and morph means forms => means many formsPolymorphism is of 2 types :- Overloading and OverridingOverloading means : Same name with in same class >in this case method name should be same but its number of arguments or sequence of arguments should be differentgives compile time error if something wrong
Overriding means : Same name with in other class >ditto same but called with class namegives Runtime time error if something wrong
37EncapsulationVariables are taken as private and those are assigned values by public getter and setter methodsalso called data hiding classIf class have not main method inside it is called entity class and also called POJO class which means Plain Old Java Object.Encapsulation class is example of entity class and it is used in Page Object Model framework
Generation of getter setter methods =>private string name;R.Click on Variable Name > Source > Generate getter & setter > select which one -> after method -> sort by -> generate 
38Inheritancethis is about to acquired properties of other class by using keyword “extends”Parent can be class or interface to child class or interfaceextends or implements / extends & implementsIs a mechanism where which one object/class acquires all the properties and behaviors of a parent object/class
all classes inherited from java.lang.object – directly or indirectly
every class extends object class which called automatically or implicitly if not mentioned otherwiseIf Object class already present in same package then extends this local class firstsystem.out.println(super.name); > super here used to call name variable from Parent class
39Overriding (in Polymorphism)@overrideOverride is kind of warring and method can be used with or w/o this keyword>> Static Methods cannot be override
public void sleep(){ }If same method is available in parent class with same arguments or with same sequence of argurments then it is called overridingIt just an indication for developer>> private method not be inheritted
super();Calling Parent class constructor>> final method cannot be override
this();Calling child class constructor
super(10, 10) or super();at a time, one constructor of parent class called in Child class and that should be metioned to before all inside child class constructorsuper(); this is also called default constructor & It called implicitly
class constructor is called in class only, not inside the methodsuper(); this(); cannot be come together as who so ever written first, same called and consider in execution
40Recursive InvocationIf one constructor called and points again to calling constructor which goes on loop then this situation is called Recursive InvocationOn the fly Object OR Anonymus Object :-If the object created without name like new Animal().run(); then is called as “On the fly OR Anonymus” Object
41UpcastingAnimal a1 = new Dog();Here Animal is the Parent class & Dog & Bird are Child classesa1 have state of instance variable & instance method of Parent class and method state of child class and execute method of child class during runtimeDuring upcasting approach, Methods execute from Child class but the variables are called from Parent class i.e. instance variablesIn other words, Object have knowledge of all the properties of Parent class and only methods of child classUPCASTING is from Parent to Child, not from child to parent while creating object, Child obj = new Parent() is wrong
Animal a2 = new Bird();Reference of Parent class and Object here created of Child classParent class called here as Reference class and child class called as object classSame name method need to be present in Parent class and in child class then child class method execute implicitly otherwise class casting need to use
If Animal extends to Bird, Bird extends to Dog then obj.Method() executes method from the first child class like dog, if not availble there then execute from next child class like bird and final from parent class if not available in any child classIf Animal extends to Bird, Bird extends to Dog then obj.Constructor() executes constructor from top most parent class, then next parent class and then finally execute from Child / current class constructorDMD (Dynamic Method Dispatch) or run time Polymorphism :-During run time, it is decided to execute method of Child class if upcasting approach used. Run from upper child class even if method is not available in lowest child classIf the methiod is static and present in child and parent class both then @override annotation is not applicable and method run from parent class only during runtime
42Class Casting((Dog)a1).runFast();Here run Fast method is not available in parent class i.e. Animal so Child class casting is need to provide to confirm executon of method in child class i.e. dog. This is called Class castingWhen method not present in parent class and have in child class and to execute from child class, class casting is required
43instanceof Operatorreturns boolean value like true or false >boolean flag = a1 instanceof Animal;This retuns true as a1 is object of Dog class which is the child class of Animal class (Parent Class)instanceof here means contains……
44Interfaceall methods are abstract inside interface. abstract keyword is optionalBody to Method is must given inside child class who implements it. Body here means logic/statements which to execute when that interface/method calledused for declaration not to define. we can implement multiple inteface in single class with keyword “implements”. if interface public then its member are public also. We can inherit interface within interface with kewords “extends”.public class abc implements Football, Basketball { }public interface Football extends Basketball { }Football and Basketball both here are interfaces
public interface Football { public void startRun(); }OR public interface Football { public abstract void startRun(); }Interface have 100% abstract methods and body / logic is to provide in class or can implement customised logic in classInterface have no constructorsprivate & protected modifiers are not allowed in interface
variables can be provide inside interface but those are “public static final”In jdk version 8 or called as 1.8 > By using default keyword, body can be given inside interface to abstract method which can be available to all child classes without implementing it in class  >default void print() { statements; } > Called with >ClassObjectName.print();
Also the public static void method can also be use in interface in jdk 1.8 >public static void print() { statements; } > Called with >interfaceName.print();
45Abstract MethodsIf only signature given for method without Body then it is called Abstract Method >abstract void setName(String name);abstract methods are not be final
By default all abstract methods are publicabstract public void multiplication();
abstract methods are meant to Overriden in child classpublic abstract void division();
46Abstract ClassThe class which can have abstract methods or solid Methods or both [Solid methods means normal method who have body]Keyword: abstract class abc { } or public abstract class abc { } It is concept of Logic hiding >Abstract classes have a rule that if the class contains even a single abstract method, it is mandatory to declare class abstract but if the class is abstract, it may or may not have abstract methods.
No Object can be created for abstract classMyFirstAbstractClass1 obj = new ClassSolid(); By upcasting approach, constructors from top most parent class run first, then from Junior class and lastly from child classwe can not use abstract with final keyword and also you can’t use abstract with static keyword.
47Random ClassReturns int from 0 to 1 upto 12 decimal points >0.012345679
This Method in Math class >Math.random();
48String ClassString V1 = “Ram”;Called String Literalcreated new object, if updated then also new object createdTwo objects created by String Literal have same value then points to same memory location
String V2 = new String(“Sham”);Called String Objectalways created new object, if updated then also new object created
In string class, whenever new value store, new object created in JVM memory every time >If, V1 = V1.concat(“123”); => Ram123 => New object created in memory, not updated the earlier stored V1 memory >This is the reason, String class called immutable
49String Interning PropertyString abc = “abc”;These two objects, created by String literal, have same value, points to same memory location in string pool and is called String interning
String xyz = “abc”;
String ddd = new String(“abc”);This always create new Object in the memory location.
Object abc & ddd are different and have different memory location>abc = ddd.intern(); >This merge the memory location of both variables having same contentNot working in code?
50index ofprintln(abc.indexOf(“c”); >returns int, first occurence of c > 2(abc.indexOf(“Gon”)); > give index of starting character
println(abc.lastIndexOf(“c”); >returns int, returns last occurence of c > 3
println(abc.indexOf(“z”); >returns int, if no value present then retuns negative value > -1
51charAt()println(abc.charAt(2)); >returns character at that index > c Index start from 0
length()abc.length();Returns int as Total count. abc is the variablecount start from 1
52compareToint x = abc4.compareTo(abc3); >retunrs int in positive and negative valueIt is not applicable to primitive type
If abc4 > abc3 =>retuns + integer
If abc4 < abc3 =>retuns – integer
If abc4 = abc3 =>retuns 0
53Garbage CollectionDelete unused objects from memory.abc = “Raghu”;
We can tel JVM for the unused object but its upto JVM when to delete itabc = null; >this tell jvm that it can delete object Ragu now and this called garbage collection
Garabage collection never be final, its depends on JVM to execute it or notabc = “Sham”;
54String Buffer ClassIts mutable classStringBuffer sb = new StringBuffer(“abc”);sb.append(“john”) > john ad up to abc in same memory location > abcJohnsb.toString(); print object value to string
(Similar have String Builder Class)New value update at same memory location of same objectStringBuffer sb = new StringBuffer();sb.replace(0, 6, “123”); >Startig from 0, at 6th index, replace 123 > abcjoh123
All values update at same location if two objects of same name, both the objects created by ‘new’ keywordsb.replace(0, sb.length(), ” “); >Startig from 0, at entire lenght, replace empty String > ans is nothing
55Loopsfor >for(initialize; Check Condition; Increment/Decrement;) { statement; }for(int i=1; i<=5; i++;) { prinln(i) }For every iteration of outside for loop, the nested for loop initializes itself(starts from beginning)
while >initialize; while(check condition) { statement; Increment / Decrement;}int i=1; while(i<=5) { prinln(i); i++; }
do – while >initialize; do{ statement; Increment / Decrement;} while(check condition);int i=1; do{ prinln(i); i++; } while(i<=5);
enhanced for loop >for(Collection_type New_Obj_Name : That_Collection_Object_ from which data to get) { statement; }for(collection_of_String ob1_name: ArrayOb2) { }
56if – else Conditionsif() { }if only one statement is to provide for condition then curly brackets not required
else if () { }
else { }
57Operators & && | ||&AND operator checks both the conditions in if conditionBinary Operatorif(i=1 & i.length()=5) > returns NPE as i is null and 2nd condition gives NPE
&&AND AND operator do not check 2nd condition in if condition if the first condition returns falseLogical operator and also called Short circuit operatorif(i=1 && i.length()=5) > returns nothing as first condition fails
|OR operator checks both the conditions in if conditionBinary OperatorWhen NPE comes, Code does not execute ahead.
||OR OR operator do not check 2nd condition in if condition if the first condition returns trueLogical Operator
58Ternary Operatorint result = val.equals(“ram”) ? 55:100;If val is equal to ram then return 55 or otherwise 100
59break; & continue;break – exit from loop >After this keyword, code written ahead does not excute for current loop also terminate the loop counter as wellcontinue – Skip one iteration / iterations as per the condition given and execute loop >After this keyword, code written ahead does not excute for current loop but start next loop
60ArraysSize must need to provideint[] arr1 = new int[5];print(arr2.toString()); returns array values. OR Arrays.toString(arr2); -> returns arrays valuesImportant Method :- Arrays.asList() :- convert Array to ListString capitalArray[] = {“Oslo”, “Stockholm”, “Washington”, “Copenhagen”, “Seoul”, “Rome”, “Madrid”};
String countryArray[] = {“Italy”, “Norway”, “South Korea”, “United States”, “Spain”, “Denmark”, “Sweden”};
arrays can be of Primitive and non primitive typeint[] arr2= {1, 2, 3, 4, 5}; //Array initializeprint(arr2); returns junk value. or called hash code valueThis method takes the array which is required to be converted into a List.  List<String> countryList = Arrays.asList(countryArray);
array have homogenous data – same type dataint [] arr2 = null; //Array initializearr2.length; – returns size. return a fixed-size list backed by the specified array. 
It has AIOBE – Array Index Out of Bound Exceptionarr2 [0] = 1; //adding element to array at this indexarr2[1].length; – returns value at that index. ??The returned list is serializable and implements RandomAccess.
Arrays are collections of objects with the same type of a defined size. We access elements in an array using an index object, and can initialize arrays both with and without elements.arr2 [1] = 2;StringObject.length(); – returns count.This method acts as a bridge between array-based and collection-based APIs, in combination with Collection.toArray()
elements to array can be provide at the time of initialize, otherwise if it declare only then elements add with index values one by oneint [] arr3; //Array declareString val = “ravi; kani; sham”;    String[] arr3 = val.split(“;”); ?
If array size given then it is still possible to add element in that but that cant be execute/print and give error out of boundint [] arr6 ;
   // NO! Initializers can only be used in declarations
//    arr6 = { 1, 2, 3, 4, 10, 11, 12 } ;		< Gives error as values can be given only when declare
61Arrays vs CollectionArraysCollection
Arrays are fixed in sizeExpands and Collapse automatically
Store same data typeHold multiple data type
Store primitve and objectsStores only object
62String to Integer thru parseIntSystem.out.println(Integer.parseInt(args[0]) + Integer.parseInt(args[1]));args here can be like >args = argumentsForMain();String args[] = {“1”, “2”};
This convert String to Integer and perform mathematical operationpublic static String[] argumentsForMain() {
String arr4[] = {“1”, “0”};
return arr4;
}		String number1 = “40”;
String number2 = “50”;		System.out.println(Integer.parseInt(number1) + Integer.parseInt(number2));
63Wrapper ClassesEight in numberStores object of primitive data type by accepting primitive valueNumber num = new Long(999999);Integer obj2 = new Integer(5);
double ll = obj2.doubleValue(); This is method in Integer class and returns value in double		AutoBoxing :-If primitive data type value input then it automatically converts to wrapper class called autoboxing
Byte, Short, Integer, Long, Float, Double, Character, BooleanNumerical classes extends from abstract Number classInteger num2 = new Integer(789);same meaning as Integer num5 = new Integer.valueOf(789); It does not accept string valueUnBoxing :-If result to get in primitive data type then it automatically convert wrapper class object to primitive data type called unboxing
Short num3 = new Short((short)100); //??int xx =Integer.parseInt(“12”); //takes in string & returns integer value
Integer num4 = new Integer(“abc”); // If string convert in integer value then it shows that otherwise gives Number Format Exception
64Collection Frameworkhave interface & classes in package java.util;store objects and not store primitrive data type
Iterable InterfaceIt has iterator() methodwhich returns object of Iterator Interface & Use to read collectiontop in hierarchy, all the collection interfaces like List, Set, Map automatically implements iterable interface
Iterator Interfacehave following methods :-ArrayList al = {1, 2, 3, 4,5 };
hasNext()returns boolean, to check if there is element in collectioniterator itr = al.iterator(); iterator methods returns object of iterator interface from collection
next()returns object of collectionwhile(itr.hasNext())
remove()returns void, remove element from collection{System.out(itr.next()); }
Collection InterfaceCollection coll = new ArrayList(); Collection Print all values but Array print Junk Value and Collection have methods >.add(“abc”)returns boolean >> [add element] to collection
.remove(“abc”)returns boolean >> [remove element] from collection
.contains(“abc”)returns boolean >> used to search an element
.clear()returns void >> remove all elements from Collection
.isEmpty()returns boolean
.size()returns int >> total nos of Elements in Collection
Collections.sort(List_Object) & Collections.reverseOrder();Sort the List in accending order & reverse the order of current object
Interfaces of Collection down in Hierarchy :-List InterfaceSet InterfaceMap Interface
can have duplicate elementsno duplicate elementsElements in Key Value pair, cant have duplicate KeysMap object need to convert in Set object to read via Map.Entry Interface
have Methods >add(1, “abc”) > insert abc at index 1 and shift earlier elements to next index, returns voidhave Methods >add(1, “abc”) > returns false if duplicate value added in collectionhave Methods >Set<Map.Entry<Integer,String>> setObj = mapObj.entrySet();, Set<Integer> setObj = mapObj.keySet();
get(5) > returns value at index 5entrySet() > returns all entries
set(1, “xyz”) > replace xyz at index 1keySet() > return all Keys
indexOf(“abc”) > return index of first occurrence of value abcput(Key, Value) > add entry in Map object
lastIndexOf(“abc”) > return index of last occurrence of value abcentry(Key, Value)
get(Key) > return value at that key
getKey() > return Key
getValue() > return Key Value at key in just above method
have classes :-Java new generic collection allows you to have only one type of object in a collection.
ArrayList<String> al=new ArrayList<String>();		have classes :-have classes :-
ArrayList Class >maintain insertion orderHashSet >returns element in Random Order due to mechanism Hashing (each object awarded hash code value which then return in accending order), allow one null valueHashMap >returns keys in Random Order, have one null key
LinkedList Class >maintains insertion order & have methods :- getFirst(); getLast(); addFirst(); addLast(), addAll(object)LinkedHashSet >returns element in inserted Order, allow one null valueLinkedHashMap >returns keys in inserted Order, have one null key
Vector Class >its Synchronised Class and hence slowSorted Set Interface >Sorted Map Interface >
TreeSet Class >returns element in accending Order, contains one type of elements only, does not allow null valueTreeMap Class >returns keys in accending Order, no null key
65Exception HandlingException come during runtime which abruptly stops the execution of programtry { } catch(Exception e) { System.out.println(e.getClass().getName() + ” ” + e.getMessage()); } finally { }method() throws FileNotFound, NullPointerException or Exception {} > this provide multiple exceptionIf the exception is handled in corresponding catch block, then normal flow of the program continues after executing “finally” blockIf the exception is not handled, then the program ends execution abruptly after executing “finally” block Error Class Exceptions :-
When exception occurs inside method, it create Exception object and handover it to JVM, If exception handling not used in code then JVM handover exception to default exception handler which show exception detail in console and abruptly close the program.multiple catch can be used with one try, Only finally can also be use with try w/o catchmethod() throws Throwable { } < it means same as Exception, which is equal to throw Exception {}throws or throw > throw new RuntimeException(“delibrate end”);1) OutOfMemory
Some Types of Exception :-Exception is the parent class of All type of Exceptions. catch(Exception e) is the top in hierarchy and its always comes down in line while writing code as when execution transfer to this then it catches the error and abruptly close the furthur execution of codecompile time exception – called checked exceptionthrow is used to deliberately/explicitly end the execution of code like >2) VirtualMachineError
1) Airthmetic Exception3) AssertionError
2) NullPointer Exception
3) ArrayIndexOutOfBounds Exception
4) Runtime Exceptioncatch(RuntimeException e) { Print}Runtime exception – called unchecked exception
5) Exception
6) NoSuchElementFound Exception
7) FileNotFound Exception
8) NumberFormat ExceptionUnchecked Exceptions >><< Checked Exceptions
File Input, File Reader & exception Message try
{
File file = new File(“\\user\\abc”);
FileReader fr = new FileReader(file);
}
catch(Exception e)
{
System.out.println(e.getClass().getName() + ” –> ” + e.getMessage());
}		java.io.FileNotFoundException –> \user\abc (No such file or directory)