Question

I am newbie in java but I think I have done well teaching myself in these few weeks. But now I am stuck at this loop.

Here is a method from one of my class. To help me debug, I have added “myString” string and “syntax” list inside this method to demonstrate what is happening and to keep it simple, at least for now.

public void getIndex(){
    String myString = "2 2 + 3 5";
    String[] syntax = myString.split(" ");

    for (int index = 0; index < syntax.length; index++){
        System.out.println("current index is: " + index);
        System.out.println("It has: " + syntax[index]);
        // these print statements are made to help me debug
        if (syntax[index] == "+"){
            indexNeeded = index;
            break;
        }
    }
    System.out.println("Index Needed: " + indexNeeded);   

As you can see inside the loop, I want to break the “for loop” when the element of the list, “syntax” is “+”.
(I am showing “+” here but it can be anything in the actual program.)

Here is the output, when run this method:

current index is: 0
It has: 2
current index is: 1
It has: 2
current index is: 2
It has: +
current index is: 3
It has: 3
current index is: 4
It has: 5
Index Needed: 0

The loop should have stopped when it found “+” but it seems that “if statement” is not working at all, and hence “indexNeeded” hasn’t changed.

It’s a simple method but what am I doing wrong here?

Answer 1

You’re trying to compare strings with ==. That doesn’t work, you need to use .equals():

change:

syntax[index] == "+"

to

syntax[index].equals("+")

== only returns true when both objects refer to the same instance. equals() will return true when the contents of the string are the same. This is what you want.