Method and Type of methods

Method:

 

• Method is a sub block of a class that contains logic of that class.
• logic must be placed inside a method, not directly at class level, if we place logic at class level compiler throws an error.
• So class level we are allowed to place variables and methods.
• The logical statements such as method calls, calculations and printing related statements must be placed inside method, because these statements are considered as logic.

1. package com.instanceofjava;
2. class sample{
3.  
4. int a;
5. int b;
6.  
7. System.out.println("instance of java"); // compiler throws an error.
8.  
9. }
10.  

1. package com.instanceofjava;
2. class sample{
3.  
4. static int a=10;
6.    
7. public static void main(String args[]){
8. 
   
9. System.out.println(a); // works fine,prints a value:10
10.  
11.  }
12. }

Method Terminology:

1.Method Prototype:

• The head portion of the method is called method prototype.

1. package com.instanceofjava;
2. class sample{
3.  
4. static int b=10;
6.    
7. public static void main(String args[]) // ->method prototype.
8. {
9. 
   
10. System.out.println(b); 
11.  
12.  }

2.Method body and logic:

• The "{ }" region is called method body, and the statements placed inside method body is called logic.

1. package com.instanceofjava;
2. class sample{
3. 
   
4. public static void main(String args[]) // ->method prototype.
5. { 
6.  
7.   int a=10,b=20; // method logic
8.   int c=a+b;  // method logic
9.   System.out.println(c);  // method logic
10.  
11.  }
12. }

3.Method parameters and arguments:

• The variables declared in method parenthesis "( )" are called parameters.
• We can define method with 0 to n number of parameters.
• The values passing to those parameters are called arguments.
• In method invocation we must pass arguments according to the parameters order and type.

1. package com.instanceofjava;
2. class sample{
3. 
   
4. public void add(int a, int b) // ->method prototype. int a, int b are parameters
5. { 
6.  
7.   int c=a+b;  // method logic
8.   System.out.println(c);  // method logic
9.  
10.  }
11.  
12. public static void main(String args[]) // ->method prototype.
13. { 
14.  
15.   sample obj= new sample();
16.   
17.  obj.add(1,2); //method call , here 1, 2 are arguments.
18. 
    
19. }
20. }

4:Method signature:

• The combination of method "name + parameters "  is called method signature

1. package com.instanceofjava;
2. class sample{
3. 
   
4. public void add(int a, int b) // ->method prototype. int a, int b are parameters
5. { 
6.  
7.   int c=a+b;  // method logic
8.   System.out.println(c);  // method logic
9.  
10.  }
11.  
12. public static void main(String args[]) // ->method prototype.
13. { 
14.  
15.   sample obj= new sample();
16.   
17.  obj.add(1,2); //method call , here 1, 2 are arguments.
18. 
    
19. }
20. }

• In the above program add(int a, int b) and  main(String args[]) are method signatures.

5. Method return type:

• The keyword that is placed before method name is called method return type.
• It tells to compiler and JVM about the type of the value is returned from this method after its execution
• If nothing is return by method then we can use "void" keyword which specifies method returns nothing.

1. package com.instanceofjava;
2. class sample{
3. 
   
4. public int add(int a, int b) // ->method prototype. int a, int b are parameters
5. { 
6.  
7.   int c=a+b;  // method logic
8.   return c;
9.  }
10.  
11. public static void main(String args[]) // ->method prototype.
12. { 
13.  
14.   sample obj= new sample();
15.   
16. int x= obj.add(1,2); //method call , here 1, 2 are arguments.
17. System.out.println(x);
18. 
    
19. }
20. }

Type of declaration of methods based on return type and arguments:

1.Method with out return type  and without arguments.

1. package com.instanceofjava;
2. class sample{
3.  
4. public void add(){
5.  
6. int a=10;
7. int b=10;
8. int c=a+b;
9. System.out.println(c);
10.  
11. }
12. 
    
13. public static void main(String args[]) // ->method prototype.
14. { 
15.  
16. sample obj= new sample();
17. obj.add();
18.  
19.  
20.  }
21. }

2.Method with out return type and with arguments.

1. package com.instanceofjava;
2. class sample{
3.  
4. public void add(int a, int b){
5.  
6. int c=a+b;
7. System.out.println(c);
8.  
9. }
10. 
    
11. public static void main(String args[]) // ->method prototype.
12. { 
13.  
14. sample obj= new sample();
15. obj.add(1,2);
16.  
17.  
18.  }
19. }

3.Method with return type  and without arguments.

1. package com.instanceofjava;
2. class sample{
3.  
4. public int add(){
5. int a=20;
6. int b=30;
7. int c=a+b;
8. return c;
9. }
10. 
    
11. public static void main(String args[]) // ->method prototype.
12. { 
13.  
14. sample obj= new sample();
15. int x=obj.add(); 
16. System.out.println(x);
17.  
18.  }
19. }

4.Method with return type and with arguments.

 

1. package com.instanceofjava;
2. class sample{
3.  
4. public int add(int a, int b){
5.  
6. int c=a+b;
7. return c;
8. }
9. 
   
10. public static void main(String args[]) // ->method prototype.
11. { 
12.  
13. sample obj= new sample();
14.  
15. int x=obj.add(1,2);
16. System.out.println(x);
17.  
18.  }
19. }

Method terminology : main method

• Lets take main method and identify method parts

1.Method Creation with body:

• The process of creating method with body is called method definition.
• Technically this method called concrete method.

1. class A{
2.  
3. public void add(){
4.  
5. }
6.  
7. }

2.Method Creation without body:

• Creating a method without body is called  "Declaring a method" or "Method declaration".
• Technically this method called "abstract method".
• In method declaration the modifier "abstract" is mandatory and also should be terminated with ";".
• Example : public void add();
• And only abstract class can have abstract method. (in interface we can use , by default all methods are abstract  )

1. abstract class A{
2.  
3. abstract  public void add();
4.  
5. }

Static and non static methods:

• If a method has static keyword in its definition then that method called static method.
• We can call static method directly from main method.
• If method does not have static keyword in its definition then it is a non static method. 
• If we want to call a non static method from main method we need object of that class
• if we want to call static method outside the class we can call by using classname.method();

1. class A{
2.  
3. public static void show(){    // static method
4.  System.out.println("static method");
5. } 
6.  
7. public void display(){      //non static method
8.  System.out.println("non static method");
9. } 
10.  
11. public static void main(String[] args){
12. show(); // static method call
13. A obj= new A();
14. obj.display(); // non static method call
15. }
16. }