Why this object reference variable is null after creating an object and assigning it to the variable?

Question

I've just started learning Java. I'm reading this book: Intro to Java Programming, Comprehensive Version (10th_Edition). In chapter 9, there's a simple program:

import java.util.Date;
public class Test {

public static void main(String[] args) {

Date date = null;

m1(date);

System.out.println(date);

}

public static void m1(Date date) {

date = new Date();

}

}

As I understand the method creates a new object and assigns It to the reference variable that was passed to It. Why does It still print null after calling the method? Thanks for your answers.

score 0 · Answer 1 · answered Oct 03 '15 at 17:26

In this method

public static void m1(Date date) {

    date = new Date();

}

You're not actually changing the real value of date. date is simply a local variable copied into the method. When m1 exits, date loses scope and is destroyed. You haven't made any real change to it (as in, the argument passed in).

Why this object reference variable is null after creating an object and assigning it to the variable?

1 Answers1