Bad constructor?

[Paul Berry]

Must be something very basic, but I can't see why this will not compile. The second attempt will compile, but not print the message in the constructor. What's going wrong?

public class MyClass
{
    public static void main( String[] args )
    {
        int i = 1;
        MyClass myClassInstance = new MyClass( i );
    }

    void MyClass( int i )
    {
        System.out.println( i );
    }
}

The errors are:


C:\Documents and Settings\Paul\Desktop\ClassTest>javac MyClass.java
MyClass.java:6: error: constructor MyClass in class MyClass cannot be applied to
given types;
MyClass myClassInstance = new MyClass( i );
^
required: no arguments
found: int
reason: actual and formal argument lists differ in length
1 error


Also, if I modify it as below (remove the constructor argument and add a message to print) then it will compile but not print the message in the constructor when run.

public class MyClass
{
    public static void main( String[] args )
    {
        int i = 1;
        MyClass myClassInstance = new MyClass();
    }

    void MyClass()
    {
        System.out.println();
        System.out.println( "in the constructor" );
    }
}

[Paul Beckett]

The main problem is that your

void MyClass(int i){}

is not a constructor definition. That is why the compilation error alludes to the "int i" constructor not being defined.

Hint: constructors do not define a return type. Have a look at the Java Tutorials for more info.

[deep semwal]

Constructors cannot have return type and that is the basic difference between a method and a constructor.

Here compiler is considering void MyClass() as a method and hence a default contructor with no arguments is provided by the compiler for your class.

And when you are passing argument in your new MyClass(i), no match is found for this constructor.

Solution: Do not give any return type keep it "public MyClass( int i )" this will work for you...

[fred rosenberger]

That's the same reason why when you remove the 'i' you don't get anything to print. with the word "void", it is not a constructor, but a method. So when you call the constructor, you get the default, no-arg constructor that the java compiler gives you for free. remove the word void from the no-arg one, and it will work.

[Campbell Ritchie]

deep semwal, welcome to the Ranch

I actually think it is a confusing feature that methods with the same identifier as the class are allowed at all. But it's too late to change now.

[deep semwal]

thank you.. campbell ritchie.

yes it is confusing.. but that is the way it is...

[Paul Berry]

Oh yeah....no return type. Well that killed an hour this morning trying to figure out.

Thank you all!