在Eclipse中使用相等运算符（==）进行字符串比较时突出显示

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

Answer 3

I disagree with previous answers - it is a bug in eclipse and you can vote for it here : https://bugs.eclipse.org/bugs/show_bug.cgi?id=39095 .

Eclipse can very well warn you when you compare Strings with == as this is seldom what you wanted (or what the original author wanted).