Internal implementation of equals

[Neelima Mohan]

Hi,

Just wanted to know how equals() method in String class is implemented?
anybody got a chance to look at the original implementation?

Thanks,
Neelima

[Danish Sualeh]

Downloading the source code would be the best thing to do.

Is there any specific doubt that you have in mind regarding the implementation of equals method ?

[Jesper de Jong]

You don't even need to download the source code separately; you can find it in the src.zip file that's in your JDK installation directory.

[Muhammad Khojaye]

I find http://www.docjar.com/ to be useful for looking the classes source code.

[Neelima Mohan]

hey thanks!

[Tracy Tse]

Jesper Young wrote:You don't even need to download the source code separately; you can find it in the src.zip file that's in your JDK installation directory.

yes,right there , afer i reading the source code, i found it quite straightforward.

First of all ,test if the two object refers to the same one,if not,then check out the characters one by one .

Below is the implementation details.

   /**
     * Compares this string to the specified object.  The result is {@code
     * true} if and only if the argument is not {@code null} and is a {@code
     * String} object that represents the same sequence of characters as this
     * object.
     *
     * @param  anObject
     *         The object to compare this {@code String} against
     *
     * @return  {@code true} if the given object represents a {@code String}
     *          equivalent to this string, {@code false} otherwise
     *
     * @see  #compareTo(String)
     * @see  #equalsIgnoreCase(String)
     */
    public boolean equals(Object anObject) {
	if (this == anObject) {
	    return true;
	}
	if (anObject instanceof String) {
	    String anotherString = (String)anObject;
	    int n = count;
	    if (n == anotherString.count) {
		char v1[] = value;
		char v2[] = anotherString.value;
		int i = offset;
		int j = anotherString.offset;
		while (n-- != 0) {
		    if (v1[i++] != v2[j++])
			return false;
		}
		return true;
	    }
	}
	return false;
    }  

Hope this helps!

[Campbell Ritchie]

Tracy Tse wrote: . . . First of all ,test if the two object refers to the same one,if not,then check out the characters one by one . . . .

You missed out the middle stage: check whether the other object is a String. Since String is a final class, it is safe to use instanceof.