How Can I Call One Constructor from Another in Java?

Calling One Constructor from Another in Java

In Java, it is possible to call a constructor from another within the same class. This can be useful in various scenarios, such as initializing an object with values provided by a parent constructor or customizing the object's state based on specific criteria.

To call a constructor from another, simply use the this keyword followed by the name of the other constructor and its parameters, as shown in the following example:

public class Foo {
    private int x;

    public Foo() {
        this(1);  // Call the Foo(int x) constructor with the value 1
    }

    public Foo(int x) {
        this.x = x;
    }
}

In this example, the default constructor Foo() calls the Foo(int x) constructor with the value 1. Consequently, when a Foo object is created without specifying any arguments, its x field will be automatically set to 1.

It's important to note that you can only chain to one constructor, and this call must be the first statement in your constructor body. Additionally, if you need to call a constructor from a superclass, use super instead of this.

For instance, consider the following scenario:

public class Animal {
    private String name;

    public Animal(String name) {
        this.name = name;
    }

    public Animal() {
        this("Default Animal");  // Call the Animal(String name) constructor with the default name "Default Animal"
    }
}

In this case, both constructors, one with a parameter and one without, call the superclass constructor with the name parameter or a default value, respectively. This allows you to initialize the name property for all Animal objects.

By leveraging the ability to call one constructor from another, developers can create complex class hierarchies with customizable object initialization and ensure a consistent and predictable state for newly created objects.

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