在Java中使用collection.sort对字符串进行排序

Question

I am a beginner in Java and I am having a problem sorting String. I know using Collections.sort it will sort String with case-sensitive by default but the uppercase ones always come in the front because it always compares the ASCII values.

If I want to keep lowercase String in front of uppercase ones, is there a clean way to implement it in Java using Collections.sort ?

For example, to sort "java Python ruby C" into "java ruby C Python".

Thanks in advance.

Answer 1

You should implement your own Comparator to define such an ordering:

Collections.sort(list, new Comparator<String>() {
    @Override
    public int compare(String s1, String s2) {
        if (/* s1 is lower case and s2 is upper case */) {
            return 1;
        }

        if (/* s1 is upper case and s2 is lower case */) {
            return -1;
        }

        return s1.compareTo(s2);
    }
});

Answer 2

Of course you can use a Comparator . Use Collections.sort(List<String> x,Comparator comp)

Answer 3

This is achieved by creating a Comparator that will impelemt the compare method.

Here is example of using AgeComparator:

import java.util.Comparator;

public class HeightComparator implements Comparator<Object> {

    @Override
    public int compare(Object o1, Object o2) {
        int p1 = ((Person)o1).height;
        int p2 = ((Person)o2).height;
        return p1 - p2;
    }
}

Now all that left is to pass our custom comparator with the collection we want to compare.

Collections.sort(peoples, new AgeComparator())

More on Comparators and Comparable can be read HERE .

Answer 4

arshajii's answer is solid. Here're the two minor conditional statements:

Collections.sort(list, new Comparator<String>() {
    @Override
    public int compare(String s1, String s2) {
        if (s1.toLowerCase().equals(s1) && s2.toUpperCase().equals(s2)) {
            return 1;
        }

        if (s1.toUpperCase().equals(s1) && s2.toLowerCase().equals(s2)) {
            return -1;
        }

        return s1.compareTo(s2);
    }
};