CODEWITHSUNDEEP
java
user2022068
user2022068

Reputation:

Java - return null or string by function parametr without if

Simple quesion but can't find the answer. I have a function

private Srting getStrOrNull(String str){
 if (str==null) return null;
 else{
  return "#"+str+"#";//ANY STRING MODIFICATION
 }
}

Can I modify this function in that way that not to use any if,switch clause? For example using hashmap etc.

I'll explain what for I need it. I have 1000s rows in database and for example to determine icon according to state for every row I do this way.

private HashMap<Int,String> iconPaths;

public String getIconPathByState(int id){
 return iconPaths.get(id)
}

I don't use any switches and ifs to do it as faster as possible as this function will be called 1000s times.

Upvotes: 0

Views: 105

Answers (3)

Iłya Bursov
Iłya Bursov

Reputation: 24146

Here is one approach which you can use sometimes, it will be slower in this artificial example with "#"+..., but main idea could be useful:

private final static String getStrOrNull(final String str) throws Exception {
    // first step prepare table for different states:
    // 0 - input value is null
    // 1 - input value is some not null string
    // in single thread application you can move this array out of the function as static variable to avoid memory allocation
    final Callable<String>[] func = new Callable[2];

    func[0] = new Callable<String>() {
        @Override
        public String call() {
            return null;
        }
    };

    func[1] = new Callable<String>() {
        @Override
        public String call() {
            return str.toLowerCase(); // any other string modification
        }
    };

    // now we need to convert our input variable into "state" (0 or 1)
    // to do this we're inserting string into set
    // if string is not null - it will be in map, final size will be 1
    // if string is null - we will remove it via remove(null), final size will be 0
    final Set<String> set = new HashSet<String>();
    set.add(str);
    set.remove(null);

    return func[set.size()].call();
}

here is another method how you can convert input variable into 0 or 1:

int i = System.identityHashCode(str); // returns 0 for null, non zero for all other values, you can also use unsafe getaddr
// converts 0 to 0, any non-zero value to 1:
int b = ((i >>> 16) & 0xffff) | (i & 0xffff);
b = ((b >>> 8) & 0xff) | (b & 0xff);
b = ((b >>> 4) & 0xf) | (b & 0xf);
b = ((b >>> 2) & 0x3) | (b & 0x3);
b = ((b >>> 1) & 0x1) | (b & 0x1);

return func[b].call();

Upvotes: 2

Timothy Wright
Timothy Wright

Reputation: 351

This is premature optimization. Today's processors, like the i7, perform 100,000 millon instructions per second. 1000's of instructions is lost in the noise.

If you really think you need to speed it up, don't guess. Measure.

http://docs.oracle.com/javase/8/docs/technotes/guides/visualvm/index.html

Upvotes: 3

MTilsted
MTilsted

Reputation: 5545

The code "#"+str+"#" is going to take at least 100 times as long as the compare, so I think you are optimizing the wrong part here.

Upvotes: 3

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