Java6

Circle

public class Circle {
// double radius;  
 
// public void area(){
//     System.out.println(3.14*radius*radius);
// }
 
   public double square(double radius){//4
      return radius * radius;//16
   } 
 public void area(double radius){//4
     System.out.println(3.14*square(radius));//16*3.14
 }
 
}

Main

/*
-NewClass2
 */
public class Main {
    public static void main(String[] args) {
        NewClass2 n = new NewClass2();
        n.sayHi();//calling
        n.sayHello("marwa",1);
//        int z = n.getValue();
//        System.out.println(z);
        
      //  System.out.println(n.getValue());
        
        String s = n.isPositive(n.getValue());
        System.out.println(s);
    }
  
}

Main2

/*
NewClass3
 */
public class Main2 {
    public static void main(String[] args) {
        NewClass3 n = new NewClass3();
        n.userInput();
    }
 
}

NewClass

public class NewClass {
    //member variable
     double height ;
    public static void main(String[] args) {
        //local variable
        int sum = 0;
    }
  
}

NewClass1

public class NewClass1 {
   /*
    member variables
    
    */
    
    /*
        constructors
    
    
    */
    
    /*
    
    
            methods
    */
    
}

NewClass2

/*
    modifier return-type meth-name (parameters){
        statements
        
    }

return type: void or any DT
parameters : int x, String s,
                
 */
public class NewClass2 {
  //void and no-parameters
 public void sayHi(){
     System.out.println("Hi");
 }
 
 //void , with parameter
 public void sayHello(String name, int i){
     System.out.println("Hello "+name); 
 }
 //return , no -parameter
 public int getValue(){
  
     return 3*8/1; 
 }
 
 //return , parameter
 public String isPositive(int x){
 
     return x>=0?"+ve":"-ve" ; 
 }
}

NewClass3

import java.util.Scanner;

/*

 */
public class NewClass3 {
    boolean b = true;
    public void userInput() {
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter 1st number");
        int x = sc.nextInt();
        System.out.println("Enter 2nd number");
        int y = sc.nextInt();
        System.out.println("Enter operator");
        String op = sc.next();

        int result = calc(x, y, op);
        if(b)
        System.out.println(result);

    }

    public int calc(int x, int y, String op) {
        int result = 0;
        switch (op) {
            case "+":
                result = x + y;
                break;
            case "-":
                result = x - y;
                break;
            case "*":
                result = x * y;
                break;
            case "/":
                if (y != 0) {
                    result = x / y;
                } else {
                    b = false;
                    System.out.println("Can't divid by zero");
                }
                break;
            default:
                b = false;
                System.out.println("Unknown operator");
        }

        return result;
    }
}

Test

/*
Main Class
 */
public class Test {
    public static void main(String[] args) {
//        Circle c = new Circle();
//        c.radius = 2.3;
//        
//        Circle c1 = new Circle();
//        c1.radius = 1.0;
//        
//        
//        Circle c2 = c;
//        c2.radius = 2.1;
//        
//        
//        c1.area();
        
        
//        System.out.println(3.14*c.radius*c.radius);//3.14*2.1*2.1
//        System.out.println(3.14*c1.radius*c1.radius);//3.14*1.0*1.0
//        System.out.println(3.14*c2.radius*c2.radius);//3.14*2.1*2.1
        
        
//        c = null;
//        c2 =null;
//        
//        System.out.println("Hi");
//        System.out.println("Hi");
//        System.out.println("Hi");
//        System.out.println("Hi");
//        System.out.println("Hi");
//        System.out.println("Hi");
//        System.out.println("Hi");
       // System.out.println(3.14*c2.radius*c2.radius);//3.14*2.1*2.1

        
    }
  
}

Test2

/*
Circle
 */
public class Test2 {
    public static void main(String[] args) {
       Circle c = new Circle();
//        c.radius = 4.0;
//        c.area();
       
       c.area(4.0);
        
    }
}