Example 1: Java program to call one constructor from another
class Main {
int sum;
// first constructor
Main() {
// calling the second constructor
this(5, 2);
}
// second constructor
Main(int arg1, int arg2) {
// add two value
this.sum = arg1 + arg2;
}
void display() {
System.out.println("Sum is: " + sum);
}
// main class
public static void main(String[] args) {
// call the first constructor
Main obj = new Main();
// call display method
obj.display();
}
}
Output
Sum is: 7
In the above example, we have created a class named Main. Here, you have created two constructors inside the Main class.
Main() {..}
Main(int arg1, int arg2) {...}
Inside the first constructor, we have used this keyword to call the second constructor.
this(5, 2);
Here, the second constructor is called from the first constructor by passing arguments 5 and 2.
Note: The line inside a constructor that calls another constructor should be the first line of the constructor. That is, this(5, 2)
should be the first line of Main()
.
Example 2: Call the constructor of the superclass from the constructor of the child class
We can also call the constructor of the superclass from the constructor of child class using super()
.
// superclass
class Languages {
// constructor of the superclass
Languages(int version1, int version2) {
if (version1 > version2) {
System.out.println("The latest version is: " + version1);
}
else {
System.out.println("The latest version is: " + version2);
}
}
}
// child class
class Main extends Languages {
// constructor of the child class
Main() {
// calling the constructor of super class
super(11, 8);
}
// main method
public static void main(String[] args) {
// call the first constructor
Main obj = new Main();
}
}
Output
The latest version is: 11
In the above example, we have created a superclass named Languages and a subclass Main. Inside the constructor of the Main class, notice the line,
super(11, 8);
Here, we are calling the constructor of the superclass (i.e. Languages(int version1, int version2)
) from the constructor of the subclass (Main()
).