Tags: Interview , J2SE

Its one of the popular Interview question asked to Java developer with 0 - 1 year experience. We'll understand method overloading followed by method overriding.

Method Overloading

Source code (MethodOverload.java)

/**
 * Example of method overloading
 *
 * @author javaQuery
 * @date 5th October, 2016
 * @Github: https://github.com/javaquery/Examples
 */
public class MethodOverload {

    public int x = 0;

    /**
     * Method overloading - Same method name(getAndIncrement) with no parameter.
     * Increment x by 1.
     *
     * @return
     */
    public int getAndIncrement() {
        x = x + 1; // you can also use like x = getAndIncrement(1);
        return x;
    }

    /**
     * Method overloading - Same method name(getAndIncrement) with parameter.
     * Increment x by given count(value).
     *
     * @param add
     * @return
     */
    public int getAndIncrement(int add) {
        x = x + add;
        return x;
    }

    public static void main(String[] args) {
        MethodOverload methodOverload = new MethodOverload();
        System.out.println("calling 'getAndIncrement()': " + methodOverload.getAndIncrement());
        System.out.println("calling 'getAndIncrement(int add)': " + methodOverload.getAndIncrement(2));
    }
}

Output

calling 'getAndIncrement()': 1
calling 'getAndIncrement(int add)': 3

---

Method Overriding
In case of class(sub-class: AddAndDisplay) extends/implements other class/interface (super-class: Addition).
Note: Overriding is used when you don't want to use default implementation provided by parent class and will write your own piece of implementation in overridden method.

Source code (Addition.java)

/**
 * Example of method overriding.
 *
 * @author javaQuery
 * @date 6th October, 2016
 * @Github: https://github.com/javaquery/Examples
 */
public class Addition {

    /**
     * Add two numbers and return the result.
     * @param x
     * @param y
     * @return 
     */
    public int add(int x, int y) {
        return x + y;
    }
}

Source code (AddAndDisplay.java)

/**
 * Example of method overriding.
 *
 * @author javaQuery
 * @date 6th October, 2016
 * @Github: https://github.com/javaquery/Examples
 */
public class AddAndDisplay extends Addition {

    /**
     * Method override of class Addition.
     * We're overriding 'add' method because we want to print
     * values of 'x' and 'y' to console along with the 'result'.
     * @param x
     * @param y
     * @return
     */
    @Override
    public int add(int x, int y) {
        int result = x + y;
        System.out.println("(x:" + x + ",y:" + y + ")");
        System.out.println("result: " + result);
        return result;
    }
}

Source code (MethodOverride.java)

/**
 * Example of method overriding.
 *
 * @author javaQuery
 * @date 6th October, 2016
 * @Github: https://github.com/javaquery/Examples
 */
public class MethodOverride {
    public static void main(String[] args) {
        /* Add two number using super class Addition's add method */
        Addition addition1 = new Addition();
        int result = addition1.add(20, 30);
        System.out.println("calling Addition.add(int x, int y)");
        System.out.println("result: " + result);
        System.out.println("********************************************");
        
        System.out.println("calling AddAndDisplay.add(int x, int y)");
        Addition addition2 = new AddAndDisplay();
        /**
         * Notice: We created object of 'Addition' using 'AddAndDisplay'.
         * 
         * So when we call Addition.add(int x, int y) method it'll execute
         * AddAndDisplay.add(int x, int y) method because 'add' is 
         * overridden. 
         * 
         * It'll hide the superclass Addition's add method and execute
         * subclass AddAndDisplay's method.
         */
        addition2.add(10, 20);
    }
}

Output

calling Addition.add(int x, int y)
result: 50
********************************************
calling AddAndDisplay.add(int x, int y)
(x:10,y:20)
result: 30

Tags: Interview , J2SE