Java常用工具类-集合排序

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？ B
   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
4. 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

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<String>();
		list.add("orange");
		list.add("tomato");
		list.add("apple");
		list.add("litchi");
		list.add("banana");
		System.out.println("排序前");
		for(String n:list){
			System.out.print(n+" ");
		}
		System.out.println("排序后");
		Collections.sort(list);
		for(String n:list){
			System.out.print(n+" ");
		}
       
    }
}

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：
   

/**
*学生类
*/
public class Student {
	private int stid;
	private String name;
	private int age;
	public int getStid() {
		return stid;
	}
	public void setStid(int stid) {
		this.stid = stid;
	}
	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 stid, String name, int age) {
		super();
		this.stid = stid;
		this.name = name;
		this.age = age;
	}
	@Override
	public String toString() {
		return "[学号：" + stid + ", 年龄" + age + ", 名字：" + name + "]";
	}
}

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) {
		List<Student> stList=new ArrayList<Student>();
		//添加
		stList.add(new Student(40,"peter",21));
		stList.add(new Student(26,"angel",15));
		stList.add(new Student(24,"tom",26));
		System.out.println("按名字排序前：");
		for(Student st:stList){
			System.out.println(st);
		}
		//匿名内部类
		Collections.sort(stList, new Comparator<Student>(){
			@Override
			public int compare(Student o1, Student o2) {
				String name1=o1.getName();
				String name2=o2.getName();
				int n=name1.compareTo(name2);
				return n;
			}
		});
		System.out.println("按名字升序排序后：");
		for(Student st:stList){
			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：
   

/**
*员工类
*/
public class Employee implements Comparable<Employee> {
	private String id;
	private String name;
	private double salary;
	public String getId() {
		return id;
	}
	public void setId(String id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public double getSalary() {
		return salary;
	}
	public void setSalary(double salary) {
		this.salary = salary;
	}
	public Employee(String id, String name, double salary) {
		super();
		this.id = id;
		this.name = name;
		this.salary = salary;
	}
	public Employee() {
		super();
	}
	@Override
	public String toString() {
		return "员工 [编号：" + id + ", 姓名：" + name + ", 工资：" + salary + "]";
	}
	@Override
	public int compareTo(Employee o) {
		double salary1=this.getSalary();
		double salary2=o.getSalary();
		int n=new Double(salary2-salary1).intValue();
		return n;
	}
}

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

public class EmployeeTest {

	public static void main(String[] args) {
		List<Employee> emList=new ArrayList<Employee>();
		emList.add(new Employee("emp001","张三",1800f));
		emList.add(new Employee("emp002","李四",1600f));
		emList.add(new Employee("emp003","王五",2100f));
		System.out.println("排序前:");
		for(Employee em:emList){
			System.out.println(em);
		}
		Collections.sort(emList);
		System.out.println("排序后:");
		for(Employee em:emList){
			System.out.println(em);
		}

	}

}