Single Inheritance for Classes in Java

Until now, all my previous articles have covered classes, methods and constructors.  In this article, I shall introduce you to the concept of inheritance and working with single inheritance.

Using your NetBeans IDE, create a new application named “SampleOOPApplication.”  Add a “Java Package” called “MyPack.”  Create a JFrame form called “test.java” and add two more Java classes (“first.java” and “second.java”) to the existing project. Add controls to your form so that it looks something like the following image. 

Modify your code in “first.java” so that it looks something like the following:

  public class First {

    int x=0;
    int y=0;

    /** Creates a new instance of First */
    public First() {
    }

    public void setValues(int m, int n) {
        x = m;
        y = n;
    }

    public int getSum() {
        int t;
        t = x + y;
        return t;
    }
  }

Modify your code in “second.java” so that it looks something like the following:

  public class Second extends First {

    /** Creates a new instance of Second */
    public Second() {
    }

    public int getProduct() {
        int p;
        p = x * y;
        return p;
    }
  }

Now, go back to the frame “test.java.”  Double click to open it and finally double click on the button to open source view.  Within the source view, modify your “buttonActionPerformed” in such a way that it looks like the following:

  private void btnShowActionPerformed(java.awt.event.ActionEvent evt) {
  // TODO add your handling code here:
        Second obj1 = new Second();
        obj1.setValues(10,20);
        int r;
        r = obj1.getSum();
        this.lblMsg.setText("Sum = " + String.valueOf(r));
        r = obj1.getProduct();
        this.lblMsg2.setText("Product = " + String.valueOf(r));
    }                    

The next section will explain the above code.