About comparing two strings

Question

Possible Duplicate:
How do I compare strings in Java?

I'm new to programming, and I'm using java. Here's a program I wrote:

class HelloApp {

    static String hi;

    public static void main(String[] args) {
        int length = args.length;
        if (length > 0) {
            hi = args[0];
            sayHi();
        }
    }

    static void sayHi() {
        if (hi == "hello") {
            System.out.println("Hello!");
        }
    }
}

My question is: Why doesn't inputting "java HelloApp hello" make "Hello!" appear on the next line?

Java requires .equals() method for String class equality test. == is used to compare if two classes refer to the same data. — Scooter, Oct 14 '12 at 07:22
why was this migrated to programmers? there are a billion "comparing strings in java" threads on SO ..? — Thousand, Oct 14 '12 at 10:49

Eng.Fouad · Answer 1 · 2012-10-14T08:45:58.773

10

if (hi == "hello") {

should be:

if (hi.equals("hello")) {

== checks if the two references are pointing to same object in the heap, while equals() checks if the two String references are pointing to objects that having the same String value.

edited Oct 14 '12 at 08:45

answered Oct 14 '12 at 07:21

Eng.Fouad

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Using FindBugs, [you can automatically detect errors like these](http://findbugs.sourceforge.net/bugDescriptions.html#ES_COMPARING_STRINGS_WITH_EQ) – Janus Troelsen Oct 14 '12 at 10:56

score 2 · Answer 2 · edited May 23 '17 at 12:34

2

you are comparing strings in a wrong way...

How do I compare strings in Java?

static void sayHi() {
    if (hi.equals("hello")) {
        System.out.println("Hello!");
    }
}

this should solve your problem..

edited May 23 '17 at 12:34

Community

1
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answered Oct 14 '12 at 07:22

maxstreifeneder

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score 2 · Answer 3 · answered Oct 14 '12 at 07:22

2

== tests reference equality, not string equality. You want to use .equals instead:

if (hi.equals("hello")) {
    ...
}

answered Oct 14 '12 at 07:22

nneonneo

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score 2 · Answer 4 · answered Oct 14 '12 at 07:22

2

You are comparing Strings incorrectly. The proper way to check for string equality is via str.equals(anotherStr), or str.equalsIgnoreCase(anotherStr). The == operator checks if the strings point to the same memory location, not the contents.

answered Oct 14 '12 at 07:22

neilvillareal

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score 1 · Answer 5 · answered Oct 14 '12 at 09:08

as neilvillareal said you can make use of str.equals(anotherStr), or str.equalsIgnoreCase(anotherStr) methods, Please refer following link for understanding difference between '==' & 'equals/equalsIgnoreCase'method : http://www.java-samples.com/showtutorial.php?tutorialid=221

About comparing two strings

5 Answers5