Java是否可以在大写的文字字符串常量上跳过.toUpperCase（）？

Question

I have a .toUpperCase() happening in a tight loop and have profiled and shown it is impacting application performance. Annoying thing is it's being called on strings already in capital letters. I'm considering just dropping the call to .toUpperCase() but this makes my code less safe for future use.

This level of Java performance optimization is past my experience thus far. Is there any way to do a pre-compilation, set an annotation, etc. to skip the call to toUpperCase on already upper case strings?

Answer 1

What you need to do if you can is call .toUpperCase() on the string once, and store it so that when you go through the loop you won't have to do it each time.

I don't believe there is a pre-compilation situation - you can't know in advance what data the code will be handling. If anyone can correct me on this, it's be pretty awesome.

If you post some example code, I'd be able to help a lot more - it really depends on what kind of access you have to the data before you get to the loop. If your loop is actually doing the data access (eg, reading from a file) and you don't have control over where those files come from, your hands are a lot more tied than if the data is hardcoded.

Any many cases there's an easy answer, but in some, there's not much you can do.

You can try equalsIgnoreCase , too. It doesn't make a new string.

Answer 2

No you cannot do this using an annotation or pre-compilation because your input is given during the runtime and the annotation and pre-compilation are compile time constructions.

If you would have known the input in advance then you could simply convert it to uppercase before running the application, ie before you compile your application.

Note that there are many ways to optimize string handling but without more information we cannot give you any tailor made solution.

Answer 3

You can write a simple function isUpperCase(String) and call it before calling toUpperCase():

if (!isUpperCase(s)) {
    s = s.toUpperCase()  
}

It might be not significantly faster but at least this way less garbage will be created. If a majority of the strings in your input are already upper case this is very valid optimization.

isUpperCase function will look roughly like this:

boolean isUpperCase(String s) {
    for (int i = 0; i < s.length; i++) {
        if (Character.isLowerCase(s.charAt(i)) {
            return false;
        }
    }
    return true;
}

Answer 4

you need to do an if statement that conditions those letters out of it. the ideas good just have a condition. Then work with ascii codes so convert it using (int) then find the ascii numbers for uppercase which i have no idea what it is, and then continue saying if ascii whatever is true then ignore this section or if its for specific letters in a line then ignore it for charAt(i)

sorry its a rough explanation