Why is my if condition comparing strings failing?

Question

This program execution is not getting inside the if condition.
please check the comment i have specified.

public static void filterObject(ArrayList<treewalker.VariableNode> variableNodeslist,
            ArrayList<treewalker.ObjectNode> objectNodeslist,
            ArrayList<treewalker.ClassNode> classNodeslist) {
        int i, j;
        for (i = 0; i < variableNodeslist.size(); i++) {
            for (j = 0; j < classNodeslist.size(); j++) {
                String argu1 = variableNodeslist.get(i).typeClass.toString();
                String argu2 = classNodeslist.get(j).name.toString();
                System.out.println(argu1);
                System.out.println(argu2);
                if (argu1 == argu2)//this if loop is not getting executed 
                {
                    System.out.println("inside for");
                }
                System.out.println("hi");
            }
        }
    }

Philip Fourie · Accepted Answer · 2012-02-22 05:43:25Z

3

Short answer:
argu1.equals(argu2) instead of argu1 == argu2

Longer answer:
The == operator in Java does a reference compare.

You want to do string comparison, use:

if (argu1.equals(argu2))

In some case the == operator might seem to do a equality check for example:

String var1 = "abc";
String var2 = "abc";

String result = ("abc" == "abc");

In this case the result is true which at first look seems to be an equality comparison but is fact a compiler optimisation where both var1 and var2 shares the same reference.

edited Feb 22, 2012 at 5:43

answered Feb 22, 2012 at 5:37

Philip Fourie

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Comments

Shashank Kadne · Accepted Answer · 2012-02-22 05:36:07Z

1

Use equals

argu1.equals(argu2)

answered Feb 22, 2012 at 5:36

Shashank Kadne

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Ashwini Raman · Accepted Answer · 2012-02-22 05:36:34Z

1

you should be doing if(argu1.equals(argu2)) for string comparision. == will compare the hashcode. For Strings, even thought the 2 strings contain the same text, their hashcodes may differ. Hence you need to use equals() to compare the string text

answered Feb 22, 2012 at 5:36

Ashwini Raman

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TotoroTotoro · Accepted Answer · 2012-02-22 05:36:47Z

1

Use String.equals() to compare your strings, not ==.

answered Feb 22, 2012 at 5:36

TotoroTotoro

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Shahzeb · Accepted Answer · 2012-02-22 05:37:26Z

1

Use if(argu1.equals(argu2)) not if(argu1==argu2)

You should never use == to compare strings.

answered Feb 22, 2012 at 5:37

Shahzeb

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