List集合排序找出其中的最大和最小值

文章目录

  • 一、先来个简单的开胃菜---最简单的排序
  • 二、list参数类型相对复杂的排序
  • 三、匿名内部类实现排序
  • 四、常规方法找出list中的最大值以及最小值
  • 五、实现Comparable接口并找出最大值和最小值
  • 六、匿名内部类实现查找list中的最大值和最小值

主要讲述对list进行排序的几种方式以及找出list中的最大值和最小值

一、先来个简单的开胃菜—最简单的排序

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

/**
 * @业务描述:
 * @package_name: PACKAGE_NAME
 * @project_name: calculator-factory
 * @author: [email protected]
 * @create_time: 2019-05-14 11:18
 * @copyright (c) ratelfu 版权所有
 */
public class ListSort {
    public static void main(String[] args) {
        List<Integer> list = new ArrayList<Integer>();
        list.add(new Integer(5));
        list.add(new Integer(13));
        list.add(new Integer(4));
        list.add(new Integer(9));
        Collections.sort(list);
        System.out.println(list.toString());
    }
}

程序运行结果:

[4, 5, 9, 13],这种简单的排序直接按照自然顺序进行升序排列

二、list参数类型相对复杂的排序

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

/**
 * @业务描述:
 * @package_name: PACKAGE_NAME
 * @project_name: calculator-factory
 * @author: [email protected]
 * @create_time: 2019-05-14 10:43
 * @copyright (c) ratelfu 版权所有
 */
public class UserMax {
    public static void main(String[] args) {
        List<User> list = new ArrayList<User>();
        list.add(new User("张三", 5));
        list.add(new User("李四", 30));
        list.add(new User("王五", 19));
        list.add(new User("陈十七", 17)); // 陈十七永远十七岁
        Collections.sort(list); // 按年龄排序
        System.out.println(list.toString());
    }
}


class User implements Comparable<User> {

    private String name; //姓名

    private int age; // 年龄


    public User(String name, int age) {
        this.name = name;
        this.age = age;
    }

    // getter && setter
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "User [name=" + name + ", age=" + age + "]";
    }

    @Override
    public int compareTo(User user) {   //重写Comparable接口的compareTo方法,
        return this.age - user.getAge();// 根据年龄升序排列,降序修改相减顺序即可
    }
}


程序运行结果:根据年龄升序排列

[User [name=张三, age=5], User [name=陈十七, age=17], User [name=王五, age=19], User [name=李四, age=30]]

三、匿名内部类实现排序

匿名内部类实现排序能本次方法范围内覆盖掉原有的类排序规则。

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

/**
 * @业务描述: 匿名内部实现Comparable接口并找出最大值和最小值
 * @package_name: PACKAGE_NAME
 * @project_name: calculator-factory
 * @author: [email protected]
 * @create_time: 2019-05-14 10:43
 * @copyright (c) ratelfu 版权所有
 */
public class UserAnonymous {


    public static void main(String[] args) {
        List<User> list = new ArrayList<User>();
        list.add(new User("张三", 5));
        list.add(new User("李四", 30));
        list.add(new User("王五", 19));
        list.add(new User("陈十七", 17)); // 陈十七永远十七岁
        Collections.sort(list, new Comparator<User>() {
            @Override
            public int compare(User u1, User u2) {
                int diff = u1.getAge() - u2.getAge();
                if (diff > 0) {
                    return 1;
                } else if (diff < 0) {
                    return -1;
                }
                return 0; //相等为0
            }
        }); // 按年龄排序
        System.out.println(list.toString());
    }
}

运行结果:[User [name=张三, age=5], User [name=陈十七, age=17], User [name=王五, age=19], User [name=李四, age=30]]

总结:以上就是list排序经常用的几种方法,前两种方法都是通过实体实现Comparable接口并重写compareTo方法,第一种方式之所以没实现接口并实现compareTo方法,通过查看Interger类源码可以看到,java已经帮我们实现好了,所以不用再次写
List集合排序找出其中的最大和最小值_第1张图片
List集合排序找出其中的最大和最小值_第2张图片
最后一种方法通过匿名内部类实现Comparator接口实现compare方法,通过自定义比较器来实现排序。


四、常规方法找出list中的最大值以及最小值


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

/**
 * @业务描述:
 * @package_name: PACKAGE_NAME
 * @project_name: calculator-factory
 * @author: [email protected]
 * @create_time: 2019-05-14 11:18
 * @copyright (c) ratelfu 版权所有
 */
public class ListSort {
    public static void main(String[] args) {
        List<Integer> list = new ArrayList<Integer>();
        list.add(new Integer(5));
        list.add(new Integer(13));
        list.add(new Integer(4));
        list.add(new Integer(9));
        Collections.sort(list);
        System.out.println(list.toString());


        Integer max = list.get(0);
        Integer min = list.get(0);

        for (int i = 0; i < list.size(); i++) {
            if (min > list.get(i)) {
                min = list.get(i);
            }
            if (max < list.get(i)) {
                max = list.get(i);
            }
        }
        System.out.println("最大值" + max);
        System.out.println("最小值" + min);

    }
}


五、实现Comparable接口并找出最大值和最小值

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

/**
 * @业务描述:常规方法实现Comparable接口并找出最大值和最小值
 * @package_name: PACKAGE_NAME
 * @project_name: calculator-factory
 * @author: [email protected]
 * @create_time: 2019-05-14 10:43
 * @copyright (c) ratelfu 版权所有
 */
public class UserMaxMin {
    public static void main(String[] args) {
        List<User> list = new ArrayList<User>();
        list.add(new User("张三", 5));
        list.add(new User("李四", 30));
        list.add(new User("王五", 19));
        list.add(new User("陈十七", 17)); // 陈十七永远十七岁
        User max = Collections.max(list);
        System.out.println("最大值"+max.toString());
        User min = Collections.min(list);
        System.out.println("最小值"+min.toString());


    }
}


class User implements Comparable<User> {

    private String name; //姓名

    private int age; // 年龄


    public User(String name, int age) {
        this.name = name;
        this.age = age;
    }

    // getter && setter
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "User [name=" + name + ", age=" + age + "]";
    }

    @Override
    public int compareTo(User user) {   //重写Comparable接口的compareTo方法,
        return this.age - user.getAge();// 根据年龄升序排列,降序修改相减顺序即可
    }
}

六、匿名内部类实现查找list中的最大值和最小值


import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

/**
 * @业务描述: 匿名内部实现Comparable接口并找出最大值和最小值
 * @package_name: PACKAGE_NAME
 * @project_name: calculator-factory
 * @author: [email protected]
 * @create_time: 2019-05-14 10:43
 * @copyright (c) ratelfu 版权所有
 */
public class UserAnonymous {


    public static void main(String[] args) {
        List<User> list = new ArrayList<User>();
        list.add(new User("张三", 5));
        list.add(new User("李四", 30));
        list.add(new User("王五", 19));
        list.add(new User("陈十七", 17)); // 陈十七永远十七岁
        User max = Collections.max(list, new Comparator<User>() {
            @Override
            public int compare(User u1, User u2) {
                int diff = u1.getAge() - u2.getAge();
                if (diff > 0) {
                    return 1;
                } else if (diff < 0) {
                    return -1;
                }
                return 0; //相等为0
            }
        });// 按年龄排序
        System.out.println("最大值"+max.toString());

        User min = Collections.min(list, new Comparator<User>() {
            @Override
            public int compare(User u1, User u2) {
                int diff = u1.getAge() - u2.getAge();
                if (diff > 0) {
                    return 1;
                } else if (diff < 0) {
                    return -1;
                }
                return 0; //相等为0
            }
        });// 按年龄排序
        System.out.println("最小值"+min.toString());
    }
}

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