2020-8-5 Java集合排序 练习

2020-8-5 Java集合排序 练习

一、选择

1. 在下面代码中的(1)(2)处可以填写（多选） （BC）
   
   A. int int
   B. Integer Integer
   C. String String
   D. string string
2. 下列说法中不正确的是： （D）
   A. Comparator接口用于对自定义类进行整体排序
   B. Comparator接口可以将Comparator传递给sort方法
   C. int compare（T o1，T o2）比较用来排序的两个对象
   D. boolean equals（Object obj）指示对象obj是否是“等于”当前对象。此方法不可以被Object类中的equals方法覆盖
3. 关于Comparable接口的说法，以下哪个是错误的？ （D）
   A. Comparable位于java.lang包
   B. 调用sort方法时，需要指定Comparable接口的实现类
   C. Comparable接口的抽象方法是 int compareTo(T t)
   D. Comparable接口还可以用于数组的排序

二、编程

1. 对英文单词进行排序，效果图如下：
   
   任务
   1、给list添加元素
   2、输出排序前list中的内容
   3、对list中的元素进行排序
   4、输出排序后list中的内容

package exercise;

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

public class StringSort {
    public static void main(String[] args) {
        List<String> list = new ArrayList<>();
        list.add("orange");
        list.add("tomato");
        list.add("apple");
        list.add("litchi");
        list.add("banana");
        System.out.println("排序前：");
        for (String lis:list){
            System.out.print(lis + "    ");
        }
        Collections.sort(list);
        System.out.println("");
        System.out.println("排序后：");
        for (String lis:list){
            System.out.print(lis + "    ");
        }
    }
}

2. 定义一个学生信息类，包括学号，姓名，年龄三个成员变量，然后按名字进行升序排序。(使用Comparator接口)
   运行效果图：
   
   任务：
   

package exercise;

public class Student {
    private int num;
    private int age;
    private String name;

    public int getNum() {
        return num;
    }

    public void setNum(int num) {
        this.num = num;
    }

    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;
    }

    public Student(int num, int age, String name) {
        this.setAge(age);
        this.setName(name);
        this.setNum(num);
    }

    public Student() {
    }

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

package exercise;

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

public class StudentTest {
    public static void main(String[] args) {
        Student stu1 = new Student(40,20,"peter");
        Student stu2 = new Student(28,5,"angel");
        Student stu3 = new Student(35,18,"tom");
        List<Student> stu = new ArrayList<>();
        stu.add(stu1);
        stu.add(stu2);
        stu.add(stu3);
        System.out.println("按名字排序前：");
        for (Student st:stu){
            System.out.println(st);
        }
        Collections.sort(stu, new Comparator<Student>() {
            @Override
            public int compare(Student o1, Student o2) {
                String name1 = o1.getName();
                String name2 = o2.getName();
                return name1.compareTo(name2);
            }
        });
        System.out.println("按名字排序后：");
        for (Student st:stu){
            System.out.println(st);
        }
    }
}

3. 定义一个员工信息类，包括编号，姓名，工资三个成员变量，要求工资定义为float类型，然后按工资进行降序排序。(使用Comparable接口)
   运行效果图：
   
   任务：
   

package exercise;

public class Employee {
    private String num;
    private String name;
    private double price;

    public String getNum() {
        return num;
    }

    public void setNum(String num) {
        this.num = num;
    }

    public String getName() {
        return name;
    }

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

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }

    public Employee(String num, String name, double price) {
        this.setName(name);
        this.setNum(num);
        this.setPrice(price);
    }

    public Employee() {
    }

    @Override
    public String toString() {
        return "员工{" +
                "编号='" + num + '\'' +
                ", 姓名='" + name + '\'' +
                ", 工资=" + price +
                '}';
    }
}

package exercise;

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

public class EmployeeTest {
    public static void main(String[] args) {
        Employee emp1 = new Employee("emp001","张三",1800);
        Employee emp2 = new Employee("emp002","李四",2500);
        Employee emp3 = new Employee("emp003","王五",1600);
        List<Employee> emp = new ArrayList<>();
        emp.add(emp1);
        emp.add(emp2);
        emp.add(emp3);
        System.out.println("排序前：");
        for (Employee em:emp){
            System.out.println(em);
        }
        Collections.sort(emp, new Comparator<Employee>() {
            @Override
            public int compare(Employee o1, Employee o2) {
                double price1 = o1.getPrice();
                double price2 = o2.getPrice();
                return (int)(price2 - price1);
            }
        });
        System.out.println("排序后：");
        for (Employee em:emp){
            System.out.println(em);
        }
    }
}