Assign instance variables with local variables - Java

Question

When you assign the value of a local string into an instance variable of a class, does it create a new object (String)?

public void setNumber(String number){
    if(number == null || number.length() != 9)
        return;
    this.number = number;
}

Do this implicity works like this:

this.number = new String(number);

No, and you can easily check. == is used to test for the same instance. If you print the value of this.number == number on the next line you will see it prints true. If you try it with the new String(number) version, it will print false. — cpp beginner
– cpp beginner, Commented Mar 31, 2018 at 9:18
Since Java strings are immutable, there is never a reason to do new String(str) implicitly. — Sergey Kalinichenko
– Sergey Kalinichenko, Commented Mar 31, 2018 at 9:23
Java has always been a bad language to learn how objects and references work... You only handle references but you never see one. People should start with C++ and eventually switch to Java. — Luke
– Luke, Commented Mar 31, 2018 at 9:28

Ousmane D. · Accepted Answer · 2018-03-31 09:17:30Z

5

The important detail to understand is when you pass a String as a parameter to the setNumber method, you're not passing an object, you're passing a reference so when you do

this.number = number;

you're taking the reference passed as a parameter and then assigning it to the this.number variable.

There is no implicit object construction in the aforementioned statement.

answered Mar 31, 2018 at 9:17

Ousmane D.

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