java wrapper获取排序最大的一条数据 java排序api

 

1. 基本数组:

//直接通过Arrays.sort工具类
int[] arr = new int[]{1,2,6,24,5,68,9,0};
          Arrays.sort(arr);

 

2.对象数组:

//通过实现Comparable接口来排序

public class student implements Comparable<student> {
    String name;
    int age;
    public student(String name, int age) {
        this.name = name;
        this.age = age;
    }

    @Override
    public int compareTo(student o) {
//        return this.age-o.age;//升序
        return o.age- this.age;//降序
    }
}

student[] arr = new student[]{ new student("a",4), new student("a",7),new student("a",1)};
        Arrays.sort(arr)

//实现Comparator接口来排序
public class student {
    String name;
    int age;
    int score;
    public student(String name, int age, int score) {
        this.name = name;
        this.age = age;
        this.score = score;
    }

    @Override
    public String toString() {
        return "student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", score=" + score +
                '}';
    }
}
   student[] arr = new student[]{
                new student("a",4,100),
                new student("b",9,100),
                new student("c",7,80),
                new student("d",20,100),
                new student("f",11,50),

        };

        Arrays.sort(arr,(o1, o2) -> {
            //这里比较的可以是多个 ,name长度比较, name直接自然顺序比较,代码显示的是成绩比较和年级比较
            int num = o2.score-o1.score;//成绩降序
            int num1 = num == 0?o1.age-o2.age:num;//  若果成绩相等的话就判断年龄  年龄升序  ;
            return num1;

        });

        for (student student : arr) {
            System.out.println(student);
        }

 结果显示:

　　

3.list排序

//简单的Integer类型
//直接用 Colletions工具类
ArrayList<Integer>  list =  new ArrayList<>();
        list.add(9);
        list.add(3);
        list.add(5);
        list.add(1);
        Collections.sort(list);
        System.out.println(list);

        结果:[1, 3, 5, 9]

 

//list存储学生对象排序
public class student {
    String name;
    int age;
    int score;
    public student(String name, int age, int score) {
        this.name = name;
        this.age = age;
        this.score = score;
    }

    @Override
    public String toString() {
        return "student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", score=" + score +
                '}';
    }
}
  ArrayList<student>  list =  new ArrayList<>();
        list.add( new student("a",4,100));
        list.add(new student("b",9,100));
        list.add(new student("d",20,100));
        list.add(new student("c",7,80));
        list.add(new student("f",11,50));
        Collections.sort(list,(o1, o2) ->{
            //这里比较的可以是多个 ,name长度比较, name直接自然顺序比较,代码显示的是成绩比较和年级比较
            int num = o2.score-o1.score;//成绩降序
            int num1 = num == 0?o1.age-o2.age:num;//  若果成绩相等的话就判断年龄  年龄升序  ;
            return num1;
            }
        );
        System.out.println(list);
    }
    //结果[student{name='a', age=4, score=100},
    // student{name='b', age=9, score=100},
    // student{name='d', age=20, score=100},
    // student{name='c', age=7, score=80},
    // student{name='f', age=11, score=50}]

4.set排序

public class student implements Comparable<student> {
    String name;
    int age;
    int score;
    public student(String name, int age, int score) {
        this.name = name;
        this.age = age;
        this.score = score;
    }

    @Override
    public String toString() {
        return "student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", score=" + score +
                '}';
    }

    @Override
    public int compareTo(student o) {
        return this.score-o.score;//score升序
    }
}
/HashSet它存储无序,离散,所以无法直接排序,只能间接排序了. 介绍两种办法 ,1转成List进行排序 2转成TreeSet进行排序
        //list前面已经排序过,这里就不展示了,这里就展示转换成ThreeSet再排序,看代码;
        HashSet<student> hashSet = new HashSet<>();
        hashSet.add( new student("貂蝉",42,100));
        hashSet.add( new student("后裔",43,100));
        hashSet.add( new student("孙悟空",4,35));
        hashSet.add( new student("阿珂",7,58));
        hashSet.add( new student("妲己",22,80));
        TreeSet<student> set = new TreeSet<>((o1, o2) ->
        {
            //排序用Comparable或者Comparator Comparable直接操作一个类,这里就不演示了, 直接上Comparator操作对象这个简便的
            //这里比较的可以是多个 ,name长度比较, name直接自然顺序比较,代码显示的是成绩比较和年级比较
            int num = o2.score-o1.score;//成绩降序
            int num1 = num == 0?o1.age-o2.age:num;//  若果成绩相等的话就判断年龄  年龄升序  ;
            return num1;
        });

        //交换元素
        for (student student : hashSet) {
            set.add(student);
        }
        System.out.println(set);
        //结果[student{name='貂蝉',age=42, score=100},
        // student{name='后裔', age=43, score=100},
        // student{name='妲己', age=22, score=80},
        // student{name='阿珂', age=7, score=58},
        // student{name='孙悟空', age=4, score=35}]


    }

　　

5.map排序