Java program calling another constructor in the constructor

Comprehensive Java Examples

In this example, we will learn how to call another constructor from a constructor in Java.

To understand this example, you should understand the followingJava programmingTopic:

• Java Constructors

• Java Methods

Example1: Java program calling another constructor from a constructor

class Main {
　　int sum;
　　//First constructor
　　Main() {
　　　　//Call the second constructor
　　　　this(5,　2);
　　}
　　//Second constructor
　　Main(int arg1, int arg2) {
　　　　//Add two values
　　　　this.sum = arg1　+　arg2;
　　}
　　void display() {
　　　　System.out.println("Total: ")　+　sum);
　　}
　　//　main class
　　public static void main(String[] args) {
　　　　//　Calling the first constructor
　　　　Main obj = new Main();
　　　　//　Call the display method
　　　　obj.display();
　　}
}

Output Result

Total:　7

In the above example, we created a class named Main. Here, you created two constructors within the Main class.

Main() {..}
Main(int arg1, int arg2) {...}

In the first constructor, we used the this keyword to call the second constructor.

this(5,　2);

Here, by passing parameters 5 And 2 Calling the second constructor from the first constructor.

Note: The line calling another constructor in the constructor should be the first line of that constructor. That is, this(5, 2) should be the first line of Main().

Example2: Calling the superclass constructor from the subclass constructor

We can also use super(), to call the superclass constructor from the subclass constructor.

//　Superclass
class Languages {
　　//Superclass constructor
　　Languages(int version1, int version2) {
　　　　if (version1　> version2) {
　　　　　　System.out.println("Latest version is: "　+　version1);
　　　　}
　　　　else {
　　　　　　System.out.println("Latest version is: "　+　version2);
　　　　}
　　}
}
//Subclass
class Main extends Languages {
　　//Subclass constructor
　　Main() {
　　　　//Calling the superclass constructor lass
　　　　super(11,　8);
　　}
　　//　main method
　　public static void main(String[] args) {
　　　　//　Calling the first constructor
　　　　Main obj = new Main();
　　}
}

Output Result

Latest version is:　11

In the above example, we create a superclass named Languages and a Main subclass. Please note the following line in the constructor of the Main class:

super(11,　8);

Here, we call the superclass constructor (i.e., Languages(int version1, int version2)

Comprehensive Java Examples