Highlight when equality operator (==) is used for string comparisons in Eclipse

Question

Is there any way I can get Eclipse to highlight the use of the == operator to test String equality? I keep mistakenly using it instead of calling .equals().

I'd really like to make that into a warning and require an @SuppressWarnings annotation to remove it, in the yet-to-happen case that I actually want to compare strings for object equality.

Are there any tools can I use to help break this bad habit at edit-time?

Answer 1

Use a static analysis tool such as FindBugs, PMD, or CheckStyle.

There are Eclipse plugins for each, along with Ant tasks, Maven plugins, etc.

Each of these has rules relating to String equality (Findbugs rule, PMD rule, Checkstyle rule).

Answer 2

The obvious answer to the question has already been given, but here is a warning that is not a direct answer: obj.equals can also fail if obj is null. So you'll often have to use code like this:

if(mystr1 != null && mystr1.equals(mystr2))

because this

if(mystr1.equals(mystr2))

would fail with a NullPointerException if mystr1 is null.

Which is why, when the comparison string is a known constant, the following syntax is often used:

if("ABCDEF".equals(mystr1))

rather than

if(mystr1.equals("ABCDEF"))

For this reason, many libraries (like apache commons / lang ) provide utility functions that combine these checks:

// this is the definition of org.apache.commons.lang.StringUtils.equals(String, String)
public static boolean equals(String str1, String str2) {
    return str1 == null ? str2 == null : str1.equals(str2);
}

// this is the definition of  org.apache.commons.lang.ObjectUtils.equals(Object, Object)
public static boolean equals(Object object1, Object object2) {
    if (object1 == object2) {
        return true;
    }
    if ((object1 == null) || (object2 == null)) {
        return false;
    }
    return object1.equals(object2);
}

Using these methods is usually safer than plain equals, unless you know for sure that one of the two objects is not null