Comparator接口

一、

例：按字典顺序对字符串进行排序

package demo6;

import java.util.ArrayList;
import java.util.Collections;

public class Test1{
    public static void main(String args[]){
        ArrayList<String> strs=new ArrayList<>();
        strs.add("xxxx");
        strs.add("aaa");
        strs.add("bbbb");
        Collections.sort(strs);//Collections用于List，Arrays用于数组
        for(String s:strs){
            System.out.println(s);
        }
    }
}

二、

public interface Comparator<T>{
    int compare(T first,T second);
}

可以定义一个实现Comparator<String>的类：

class LengthComparator implements Comparator<String>{
    public int compare(String first,String second){
        return first.length()-second.length();
    }
}

例：按长度递增顺序对字符串进行排序

package demo6;

import java.util.Arrays;
import java.util.Comparator;

public class Test1{
    public static void main(String args[]){
        String str1="xxxx";
        String str2="aaa";
        String str3="b";
        LengthComparator len = new LengthComparator();
        String[] strings=new String[3];
        strings[0]=str2;
        strings[1]=str1;
        strings[2]=str3;
        Arrays.sort(strings, len);
        for(String s:strings){
            System.out.println(s);
        }
    }
}

class LengthComparator implements Comparator<String>{
    public int compare(String first,String second){
        return first.length()-second.length();
    }
}

或者使用lambda表达式：

import java.util.Arrays;
import java.util.Comparator;

public class  Test1{
    public static void main(String[]args) throws Exception{
        String[] strs=new String[]{"xxxx","aa","bbb"};
        Comparator<String> comparator=(String first,String second)->{return first.length()-second.length();};
        Arrays.sort(strs, comparator);
        System.out.println(Arrays.toString(strs));
    }
}