Sort

Sort

1.Array.sort()

import java.io.BufferedWriter;
import java.io.OutputStreamWriter;
import java.util.Arrays;

public class Main {
    public static void main(String[] args) throws Exception {
        BufferedWriter cout = new BufferedWriter(new OutputStreamWriter(System.out));
        int[]a = {9,8,7,6,5,4,3,2,1,0};
        Arrays.sort(a,0,a.length);
        for(int i = 0;i < a.length; i++)
            cout.write(a[i]+" ");
        cout.close();
    }
}

2.自定义排序

方法一： 创建实现Comparator接口的类/匿名内部类(推荐)

Arrays.sort(T[] a, Comparator<? Super T> c)用Comparator接口实现自定义排序规则

import java.io.BufferedWriter;
import java.io.OutputStreamWriter;
import java.util.Arrays;
import java.util.Comparator;

public class Main {
    public static void main(String[] args) throws Exception {
        BufferedWriter cout = new BufferedWriter(new OutputStreamWriter(System.out));
        //不能用基本数据类型，这里要用引用类型
        Integer[]a = {1,2,7,6,5,4,3,2,9,0};
        //降序
        Arrays.sort(a,new Comparator<Integer>(){
            //重新compare方法
            public int compare(Integer a,Integer b){
                //返回值>0交换
                return b-a;
            }
        });

        for(int i = 0;i < a.length; i++)
            cout.write(a[i]+" ");
        cout.close();
    }
}

输出：

9 7 6 5 4 3 2 2 1 0 

样例2：

import java.io.*;
import java.util.Arrays;
import java.util.Comparator;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) throws Exception{
        StreamTokenizer cin = new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));
        BufferedWriter cout = new BufferedWriter(new OutputStreamWriter(System.out));

        //注意要用Integer，如果不用自定义排序，用它原本的，用int就行了
        Integer[] arr = new Integer[10];

        for (int i = 0; i < 10; i++) {
            cin.nextToken();
            arr[i] = (int) cin.nval;
        }
        Arrays.sort(arr,0,5, new Comparator<Integer>() {
            @Override
            public int compare(Integer o1, Integer o2) {
                return o2-o1;
            }
        });

        for(int i = 0;i < 10; i++)
        {
            cout.write(arr[i]+" ");
        }
        cout.close();

    }
}

方法二：基于Comparator构建Lambda 表达式

import java.io.BufferedWriter;
import java.io.OutputStreamWriter;
import java.util.Arrays;
import java.util.Comparator;

public class Main {
    public static void main(String[] args) throws Exception {
        BufferedWriter cout = new BufferedWriter(new OutputStreamWriter(System.out));
        //不能用基本数据类型，这里要用引用类型
        Integer[]arr = {0,1,2,3,4,5,6,7,8};
        //降序
        Arrays.sort(arr,(a,b)->{
            return b - a;
        });

        for(int i = 0;i < arr.length; i++)
            cout.write(arr[i]+" ");
        cout.close();
    }
}

输出：

8 7 6 5 4 3 2 1 0 

方法三：重新实现Comparator接口

import java.io.BufferedWriter;
import java.io.OutputStreamWriter;
import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception{
        BufferedWriter cout = new BufferedWriter(new OutputStreamWriter(System.out));
        Integer[] arr = {5,4,7,9,2,12,54,21,1};
        //降序
        //重新实现Comparator接口
        Arrays.sort(arr, new cmp());
        cout.write(Arrays.toString(arr));
        cout.close();
    }
}

class cmp implements Comparator<Integer>{
    public int compare(Integer o1, Integer o2) {
        // A.compareTo(B) A>B 返回1，A=B 返回0，A<B 返回-1
        // compareTo()返回值>0就交换
        // 如果o2 > o1 就交换 =>降序
        return o2.compareTo(o1);
    }
}

输出：

[54, 21, 12, 9, 7, 5, 4, 2, 1]