Java Classes Tutorial Part-2

 Java Classes Tutorial Part-2

 

 ←

 Table of contents

 

1. Method Overloading
2. Access modifiers
1. static
2. final
3. Multiple classes

 

 

 

Method Overloading

A single class can have multiple functions with same name and different parameters and different return types. 

 

example:
 

class MethodOverloadDemo
{
int add(int x, int y)
{
    return (x + y);
}
String add(String s1,String s2)
{
    return (s1 + s2);
}
public static void main(String args[])
{
    OverloadMethodDemo mod = new OverloadMethodDemo();
    mod.add("abc","xyz");
    mod.add(5,6);
}

}

 

 *** always highest datatype constructors invoked first. 

 

 Toc

Access modifiers

• static
• final

static keyword

A static keyword can be used with variable and methods. Static variable/method available with the class itself. Static variables are used only with in the static methods or in static blocks.  

 

 

 

class StaticDemo
{
    static int a; 

StaticDemo()
{
    a = 10;
}
static void display()
{
    System.out.println("a = " + a);
}
public static void main(String args[])
{
    StaticDemo d = new StaticDemo();
    StaticDemo.display();
}
}

class StaticDemo2
{
    static int c;
StaticDemo2()
{
    c++;
    System.out.println("c = " + c);
}
public static void main(String args[])
{
    StaticDemo ob1 = new StaticDemo();
    StaticDemo ob2 = new StaticDemo();
    StaticDemo ob3 = new StaticDemo();
}
}
public StaticDemo3()
{
    name = null;
    rno = 0;
}
public StaticDemo3(String n,int rn)
{
    name = n;
    rno = rn;
}
void display()
{
    System.out.println("name = " + name);
    System.out.println("Rno = " + rno);
    System.out.println("college = " + college);
}
static void change()
{
    college = "JBC";
}
public static void main(String args[])
{
    StaticDemo3 ob1 = new StaticDemo3();
    ob1.display();
    StaticDemo3.change();
    StaticDemo3 ob2 = new StaticDemo3();
    ob2.display();
}
}

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final keyword

final can be used with variable, methods, class

• final variable ----the values of variable can't be changed.
  
• final methods --- can't be redefined in child class.
  
• final class ---- can't be extended.
  

 Example

public class FinalDemo

 
{
    final float PI = 3.14f;  //final varible
    int r;
    float ac = 0.0f;
void area(){
    r = 6;
    ac = PI*r*r;
}
void display()
{
    System.out.println("ac = " + ac);
}
public static void main(String args[]){
    FinalDemo fd = new FinalDemo();
    fd.area();
    fd.display();
}
}
Output
ac = 113.04

 

 Menu

 Multiple Classes

In java, one class object can be created in another class.

In the below example, Test class creating an object of class A.  

 

--both the classes save in  Test.java and run the file Test.java

 //Test.java 
 
class A
{
    int a; 

A ( int a)
{
    this.a = a;
}
 

int square()
{
    return (a * a);
}
}

public class Test
{
public static void main(String args[]){
 

    A objA = new A(5);  // class A object created in Test class
    

    int x = objA.square();
    System.out.print("sqare = " + x); 

}
}