signature of constructor

[nirjari patel]

Do I need to specify "void" return type for constructor ?

If I tpye public TestConstructor() {}

Will it be automatically considered void by compiler ?

If I just type TerstConstructor() {}, will that be a legal name for contructor ?

Thanks

[Tom Reilly]

Do I need to specify "void" return type for constructor ?

Constructors never have return types. If you specify a return type then it is no longer a constructor. It is a method with the same name as the class.

If I tpye public TestConstructor() {}

Will it be automatically considered void by compiler ?

That is a valid constructor.

If I just type TerstConstructor() {}, will that be a legal name for contructor ?

Yes, if your class is called TerstConstructor. If your class is called TestConstructor then this will be a compiler error because the compiler will see it as a method without a return type.

[Jesper de Jong]

As Tom said, constructors don't have a return value, so you don't have to specify a return type.

In fact, constructors are not methods, even though they look like methods. A constructor is a special block of code that is called by the JVM when a new instance of the class is created.

When you specify a return type, then it's not a constructor anymore, but just a regular method. That can be tricky:

class MyClass {
    // Note: This is *not* a constructor! It's just a method that happens to have the same name as the class.
    public void MyClass() {
        System.out.println("Hello"!);
    }

    public static void main(String[] args) {
        MyClass obj = new MyClass();  // Does *not* print Hello!

        obj.MyClass();  // Call the method and print Hello!
    }
}

[Campbell Ritchie]

You can probably understand Jesper's last example better if you examine the bytecode. Use either of these instructions (which produce different displays):

javap MyClass
javap -c MyClass