Question

I have these two situations:

String s = "aa";
s = s + " aa";
    System.out.println(s);
    //......

that work fine! It prints aa aa.
But there is a problem:

String s = "aa";
this.addStringToStatement(s, " aa");
System.out.println(s);
//...
private void addStringToStatement(String statement, Object value) {
    statement += value;
}

It prints: aa.
What is the reason??
Thanks!

Answer 1

There are two issues to understand here.

1. The String append operator will create a new immutable String object. The expression s + value is a different object in memory from s.

2. In your function addStringToStatement when you execute statement += value; you aren’t changing the value of the variable s, rather you are reassigning the local pointer statement to a new String instance.

EDIT: Fixed usual noob mistake: In Java, object references are passed, not the objects themselves.