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Java How To Write A Constructor

Writing a constructor in Java is easy. Constructors are used to initialize an instance of a class. They can also be used to handle initial parameters. The constructor for a class has the same name as the class and does not have a return value. If a return value is specified it will not be treated as an actual constructor and will not be called when creating an instance of a class.

The most basic syntax looks like this:


public class MyClass{
   MyClass(){
   }

Here is an example of a simple constructor that initializes a variable.


import java.util.*;

public class Test1 {
    public int x;

    public Test1(){      // constructor
        x = 1234;        // initialize variable
    }
    public static void main( String[] args ){
        Test1 t = new Test1();
        System.out.println( t.x );
    }
}

You can also pass a parameter to a constructor like this.


public Test1(int a){     // constructor
    x = a;               // initialize variable
}

If the parameter has the same name as the class attribute that you want to set you can refer to it using the “this” keyword like this.


public Test1(int x){      // constructor
    this.x = x;           // initialize variable
}