SAX parser and String interning

Question

I noticed all Strings in DefaultHandler's event methods are interned. Would it be better to see if Strings are equals with == instead of equals()?

@Override
public void startElement(String uri, String localName, String qName,
     Attributes attributes) throws SAXException {

if(localName == "element")
// do something

// or

if(localName.equals("element"))
// do something

}

Since all String literals are interned, it should improve performance. But all the tutorials and examples I've seen use equals()

A problem I can see is if you need to use equalsIgnoreCase()

matt b · Accepted Answer · 2013-03-05 22:14:04Z

7

At least in Oracle JDK7, the very first thing String.equals(Object) does is check if the object reference is the same as the String instance:

public boolean equals(Object anObject) {
    if (this == anObject) {
        return true;
    }
    ...

So, even if == in these cases would yield correct results, the only savings you have accomplished are a method call that (almost) immediately returns. I doubt that the cost savings would be noticeable in any sort of measurement.

Even if there was some measurable cost savings, it seems like it would be a very risky optimization - to always assume that == comparisons are correct for these Strings. What if a future version of the SAX class changes behavior? Is string interning a documented feature of it's API? Sounds doubtful.

answered Mar 5, 2013 at 22:14

matt b

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1 Comment

Kyle Kroboth Over a year ago

Thanks for pointing that out. The SAX parsers I use have String interning feature, but it may change like you said.

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