1. Methods and Classes

2. Method Overloading Two or more methods within the same class that share the same name but different parameters class OverloadDemo { void test() { System.out.println("No parameters"); } void test(int a) { System.out.println("a: " + a); } void test(int a, int b) { System.out.println("a and b: " + a + " " + b); } double test(double a) { System.out.println("double a: " + a); return a*a; } class Overload { public static void main(String args[]) { OverloadDemo ob = new OverloadDemo(); double result; // call all versions of test() ob.test(); ob.test(10); ob.test(10, 20); result = ob.test(123.25); System.out.println("Result of ob.test(123.25): " + result); }

3. Method Overloading Advantage of method overloading? Method overloading increases the readability of the program. Different ways to overload the method There are two ways to overload the method in java oBy changing number of arguments oBy changing the data type

4. Method Overloading Java’s automatic type conversions Method parameter match need not always be exact. In some cases, Java’s automatic type conversions can apply in overloading. class OverloadDemo { void test() { System.out.println("No parameters"); } void test(int a, int b) { System.out.println("a and b: " + a + " " + b); } void test(double a) { System.out.println("Inside test(double) a: " + a); } class Overload { public static void main(String args[]) { OverloadDemo ob = new OverloadDemo(); int i = 88; ob.test(); ob.test(10, 20); ob.test(i); // this will invoke test(double) ob.test(123.2); // this will invoke test(double) } Output: No parameters a and b: 10 20 Inside test(double) a: 88 Inside test(double) a: 123.2

5. Method Overloading by changing the number of arguments class Calculation{ void sum(int a,int b){System.out.println(a+b);} void sum(int a,int b,int c){System.out.println(a+b+c);} public static void main(String args[]){ Calculation obj=new Calculation(); obj.sum(10,10,10); obj.sum(20,20); }

6. Method Overloading by changing data type of argument class Calculation2{ void sum(int a,int b){ System.out.println(a+b); } void sum(double a,double b){ System.out.println(a+b); } public static void main(String args[]){ Calculation2 obj=new Calculation2(); obj.sum(10.5,10.5); obj.sum(20,20); }

7. Method Overloading Why Method Overloaing is not possible by changing only the return type of method? In java, method overloading is not possible by changing the return type of the method because there may occur ambiguity. Let's see how ambiguity may occur: because there was problem: class Calculation3{ int sum(int a,int b){System.out.println(a+b); return (a+b);} double sum(int a,int b){System.out.println(a+b); return (a+b);} public static void main(String args[]){ Calculation3 obj=new Calculation3(); int result=obj.sum(20,20); //Compile Time Error } int result=obj.sum(20,20); //Here how can java determine which sum() method should be called

8. Method Overloading with Type Promotion class OverloadingCalculation1{ void sum(int a,long b){System.out.println(a+b);} void sum(int a,int b,int c){System.out.println(a+b+c);} public static void main(String args[]){ OverloadingCalculation1 obj=new OverloadingCalculation1(); obj.sum(20,20);//now second int literal will be promoted to long obj.sum(20,20,20); } Output:40 60

9. Method Overloading with Type Promotion in case ambiguity class OverloadingCalculation3{ void sum(int a,long b){System.out.println("a method invoked");} void sum(long a,int b){System.out.println("b method invoked");} public static void main(String args[]){ OverloadingCalculation3 obj=new OverloadingCalculation3(); obj.sum(20,20);//now ambiguity } Output:Compile Time Error

10. Method Overloading with Type Promotion if matching found class OverloadingCalculation2{ void sum(int a,int b){System.out.println("int arg method invoked");} void sum(long a,long b){System.out.println("long arg method invoked");} public static void main(String args[]){ OverloadingCalculation2 obj=new OverloadingCalculation2(); obj.sum(20,20);//now int arg sum() method gets invoked } Output:int arg method invoked

11. Method Overloading Polymorphism

12. Runtime Polymorphism Runtime polymorphism or Dynamic Method Dispatch is a process in which a call to an overridden method is resolved at runtime rather than compile-time. In this process, an overridden method is called through the reference variable of a superclass. The determination of the method to be called is based on the object being referred to by the reference variable.

13. Upcasting for Runtime Polymorphism When reference variable of Parent class refers to the object of Child class, it is known as upcasting. For example: class A{} class B extends A{} --------------------------------- A a = new B();//upcasting

14. Example of Runtime Polymorphism Since method invocation is determined by the JVM not compiler, it is known as runtime polymorphism. class Bike{ void run(){System.out.println("running");} } class Splender extends Bike{ void run(){System.out.println("running safely with 60km");} public static void main(String args[]){ Bike b = new Splender();//upcasting b.run(); } Output: running safely with 60km.

15. Example of Runtime Polymorphism method overriding but there was no upcasting class Bank{ int getRateOfInterest(){return 0;} } class A extends Bank{ int getRateOfInterest(){return 8;} } class B extends Bank{ int getRateOfInterest(){return 7;} } class C extends Bank{ int getRateOfInterest(){return 9;} } class Test3{ public static void main(String args[]){ Bank b1=new A(); Bank b2=new B(); Bank b3=new C(); System.out.println(“A Rate of Interest: "+b1.getRateOfInterest()); System.out.println(“B Rate of Interest: "+b2.getRateOfInterest()); System.out.println(“C Rate of Interest: "+b3.getRateOfInterest()); } Output: A Rate of Interest: 8 B Rate of Interest: 7 C Rate of Interest: 9

16. Runtime Polymorphism with data member class Bike{ int speedlimit=90; } class Honda3 extends Bike{ int speedlimit=150; public static void main(String args[]){ Bike obj=new Honda3(); System.out.println(obj.speedlimit);//90 } Output: 90 Method is overridden not the datamembers, so runtime polymorphism can't be achieved by data members. In the example we are accessing the data member by Parent reference variable which refers to the subclass object. Since we are accessing the data member which is not overridden, hence it will access the data member of Parent class always

17. Runtime Polymorphism with Multilevel Inheritance class Animal{ void eat(){System.out.println("eating");} } class Dog extends Animal{ void eat(){System.out.println("eating fruits");} } class BabyDog extends Dog{ void eat(){System.out.println("drinking milk");} public static void main(String args[]){ Animal a1,a2,a3; a1=new Animal(); a2=new Dog(); a3=new BabyDog(); a1.eat(); a2.eat(); a3.eat(); } Output: eating eating fruits drinking Milk

18. Method Overriding If subclass (child class) has the same method as declared in the parent class, it is known as method overriding Usage of Java Method Overriding Method overriding is used to provide specific implementation of a method that is already provided by its super class. Method overriding is used for runtime polymorphism

19. Rules for Java Method Overriding method must have same name as in the parent class method must have same parameter as in the parent class. must be IS-A relationship (inheritance).

20. Example of method overriding class Vehicle{ void run(){System.out.println("Vehicle is running");} } class Bike2 extends Vehicle{ void run(){System.out.println("Bike is running safely");} public static void main(String args[]){ Bike2 obj = new Bike2(); obj.run(); } Output: Bike is running safely

21. Example of method overriding class Bank{ int getRateOfInterest(){return 0;} } class A extends Bank{ int getRateOfInterest(){return 8;} } class B extends Bank{ int getRateOfInterest(){return 7;} } class C extends Bank{ int getRateOfInterest(){return 9;} } class Test2{ public static void main(String args[]){ A s=new A(); B i=new B(); C a=new C(); System.out.println(“A Rate of Interest: "+s.getRateOfInterest()); System.out.println(“B Rate of Interest: "+i.getRateOfInterest()); System.out.println(“C Rate of Interest: "+a.getRateOfInterest()); } Output: A Rate of Interest: 8 B Rate of Interest: 7 C Rate of Interest: 9

22. method overriding Can we override static method? No, static method cannot be overridden. Why we cannot override static method? because static method is bound with class whereas instance method is bound with object. Static belongs to class area and instance belongs to heap area. Can we override java main method? No, because main is a static method.

23. Method Overriding Polymorphism

24. Difference between method Overloading and Method Overriding No.Method OverloadingMethod Overriding 1) Method overloading is used to increase the readability of the program. Method overriding is used to provide the specific implementation of the method that is already provided by its super class. 2)Method overloading is performed within class. Method overriding occurs in two classes that have IS-A (inheritance) relationship. 3) In case of method overloading, parameter must be different. In case of method overriding, parameter must be same. 4) Method overloading is the example of compile time polymorphism. Method overriding is the example of run time polymorphism. 5) In java, method overloading can't be performed by changing return type of the method only. Return type can be same or different in method overloading. But you must have to change the parameter. Return type must be same or covariant in method overriding.

25. Overloading Constructors class Box { double width, height, depth; Box(double w, double h, double d) { width = w; height = h; depth = d; } Box ob = new Box(); class Box { double width, height, depth; Box(double w, double h, double d) { width = w; height = h; depth = d; } Box() { width = -1; height = -1; depth = -1; } Box ob = new Box();

26. Objects as Parameters class Test { int a, b; Test(int i, int j) { a = i; b = j; } boolean TestEqualTo(Test obj) { if(obj.a == a && obj.b == b) return true; else return false; } class PassOb { public static void main(String args[]) { Test ob1 = new Test(100, 22); Test ob2 = new Test(100, 22); Test ob3 = new Test(-1, -1); System.out.println("ob1 == ob2: " + ob1.TestEqualTo(ob2)); System.out.println("ob1 == ob3: " + ob1.TestEqualTo(ob3)); } Output: ob1 == ob2: true ob1 == ob3: false

27. Passing Parameters Passing Parameters are two types: call-by-value call-by-reference

28. call-by-value The call by value method of passing arguments to a function copies the actual value of an argument into the formal parameter of the function. In this case, changes made to the parameter inside the function have no effect on the argument class Test { void meth(int i, int j) { i *= 2; j /= 2; } class CallByValue { public static void main(String args[]) { Test ob = new Test(); int a = 15, b = 20; System.out.println("a and b before call: " + a + " " + b); ob.meth(a, b); System.out.println("a and b after call: " + a + " " + b); } Output: a and b before call: 15 20 a and b after call: 15 20

29. call-by-reference The call by reference method of passing arguments to a function copies the address of an argument into the formal parameter. Inside the function, the address is used to access the actual argument used in the call. It means the changes made to the parameter affect the passed argument. class Test { int a, b; Test(int i, int j) { a = i; b = j; } void meth(Test o) { o.a *= 2; o.b /= 2; } class PassObjRef { public static void main(String args[]) { Test ob = new Test(15, 20); System.out.println("ob.a and ob.b before call: " + ob.a + " " + ob.b); ob.meth(ob); System.out.println("ob.a and ob.b after call: " + ob.a + " " + ob.b); } Output: ob.a and ob.b before call: 15 20 ob.a and ob.b after call: 30 10

30. call-by-value & call-by-reference When a simple type (primitive type variable) is passed to a method, it is done by use of call-by-value. Object are passed by use of call-by-reference

31. Returning Objects A method can return any type of data, including class types that is object // Returning an object. class Test { int a; Test(int i) { a = i; } Test incrByTen() { Test temp = new Test(a+10); return temp; } class RetOb { public static void main(String args[]) { Test ob1 = new Test(2); Test ob2; ob2 = ob1.incrByTen(); System.out.println("ob1.a: " + ob1.a); System.out.println("ob2.a: " + ob2.a); ob2 = ob2.incrByTen(); System.out.println("ob2.a after second increase: " + ob2.a); } Output: ob1.a: 2 ob2.a: 12 ob2.a after second increase: 22

32. Recursion A method that calls itself is said to be recursive // A simple example of recursion. class Factorial { // this is a recursive method int fact(int n) { int result; if(n==1) return 1; result = fact(n-1) * n; return result; } class Recursion { public static void main(String args[]) { Factorial f = new Factorial(); System.out.println("Factorial of 3 is " + f.fact(3)); System.out.println("Factorial of 4 is " + f.fact(4)); System.out.println("Factorial of 5 is " + f.fact(5)); } Output: Factorial of 3 is 6 Factorial of 4 is 24 Factorial of 5 is 120

33. Nested/ Inner Class class within another class known as nested classe The scope of a nested class is bounded by the scope of its enclosing/ outer class it can access all the members of outer class including private data members and methods class Java_Outer_class{ //code class Java_Inner_class{ //code }

34. Nested/ Inner Class It is important to realize that an instance of Inner can be created only in the context of class Outer Inner is known only within the scope of class Outer

35. Advantage of inner classes Three advantages of inner classes : 1) it can access all the members (data members and methods) of outer class including private. 2) Nested classes are used to develop more readable and maintainable code because it logically group classes and interfaces in one place only. 3) Code Optimization: It requires less code to write.

36. Nested/ Inner Class // Demonstrate an inner class. class Outer { int outer_x = 100; void test() { Inner inner = new Inner(); inner.display(); } // this is an inner class class Inner { void display() { System.out.println("display: outer_x = " + outer_x); } class InnerClassDemo { public static void main(String args[]) { Outer outer = new Outer(); outer.test(); } OUTPUT: display: outer_x = 100

37. Nested/ Inner Class What is the difference between nested class and inner class? Ans: Inner class is a part of nested class.

38. Types of Nested classes There are two types of nested classes non-static and static nested classes.The non-static nested classes are also known as inner classes. Non-static nested class(inner class) a)Member inner class b)Annomynous inner class c)Local inner class Static nested class

39. Member inner class A non-static class that is created inside a class but outside a method is called member inner class. class Outer{ //code class Inner{ //code } we are creating msg() method in member inner class that is accessing the private data member of outer class. class TestMemberOuter1{ private int data=30; class Inner{ void msg(){System.out.println("data is "+data);} } public static void main(String args[]){ TestMemberOuter1 obj=new TestMemberOuter1(); TestMemberOuter1.Inner in=obj.new Inner(); in.msg(); }

40. Anonymous inner class A class that have no name is known as anonymous inner class in java. It should be used if you have to override method of class or interface. Java Anonymous inner class can be created by two ways: Class (may be abstract or concrete). Interface

41. Anonymous inner class example abstract class Person{ abstract void eat(); } class TestAnonymousInner{ public static void main(String args[]){ Person p=new Person(){ void eat(){System.out.println("nice fruits");} }; p.eat(); }

42. Anonymous inner class example Internal working of given code Person p=new Person(){ void eat(){System.out.println("nice fruits");} }; A class is created but its name is decided by the compiler which extends the Person class and provides the implementation of the eat() method. An object of Anonymous class is created that is referred by p reference variable of Person type. Internal class generated by the compiler import java.io.PrintStream; static class TestAnonymousInner$1 extends Person { TestAnonymousInner$1(){} void eat() { System.out.println("nice fruits"); }

43. Java Local inner class A class i.e. created inside a method is called local inner class //Java local inner class example public class localInner1{ private int data=30;//instance variable void display(){ class Local{ void msg(){System.out.println(data);} } Local l=new Local(); l.msg(); } public static void main(String args[]){ localInner1 obj=new localInner1(); obj.display(); } //Example of local inner class with local variable class localInner2{ private int data=30;//instance variable void display(){ int value=50;//local variable must be final till jdk 1.7 only class Local{ void msg(){System.out.println(value);} } Local l=new Local(); l.msg(); } public static void main(String args[]){ localInner2 obj=new localInner2(); obj.display(); }

44. Static inner class A static class i.e. created inside a class is called static nested class in java. It cannot access non-static data members and methods. It can be accessed by outer class name. It can access static data members of outer class including private. Static nested class cannot access non-static (instance) data member or method. //static nested class example with instance method class TestOuter1{ static int data=30; static class Inner{ void msg(){System.out.println("data is "+data);} } public static void main(String args[]){ TestOuter1.Inner obj=new TestOuter1.Inner(); obj.msg(); } //static nested class example with static method class TestOuter2{ static int data=30; static class Inner{ static void msg(){System.out.println("data is "+data);} } public static void main(String args[]){ ();//no need to create the instance of static nesTestOuter2.I nner.msgted class }

45. Java Programs