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
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
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
public class StringSort {
public static void main(String[] args) {
//给list添加元素
List<String> list = new ArrayList<>();
list.add("orange");
list.add("tomato");
list.add("apple");
list.add("litchi");
list.add("banana");
//输出排序前list中的内容
System.out.println("排序前:");
for (String str : list) {
System.out.print(str + " ");
}
System.out.println();
//对list中的元素进行排序
Collections.sort(list);
//输出排序后list中的内容
System.out.println("排序后:");
for (String str : list) {
System.out.print(str + " ");
}
System.out.println();
}
}
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:
public class Student {
//成员变量
private int id;
private String name;
private int age;
//构造器
public Student() {
super();
}
public Student(int id, String name, int age) {
super();
this.setId(id);
this.setName(name);
this.setAge(age);
}
//getters&setters
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
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;
}
//重写toString
@Override
public String toString() {
return "[学号:" + getId() + ", 年龄:" + getAge() + ", 姓名:" + getName() + "]";
}
}
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
public class Test implements Comparator<Student>{
@Override
public int compare(Student s1, Student s2) {
//姓名升序
String name1 = s1.getName();
String name2 = s2.getName();
int n = name1.compareTo(name2);
return n;
}
public static void main(String[] args) {
List<Student> list = new ArrayList<>();
list.add(new Student(40, "peter", 20));
list.add(new Student(28, "angel", 5));
list.add(new Student(35, "tom", 18));
System.out.println("按名字排序前:");
for (Student s : list) {
System.out.println(s);
}
Collections.sort(list, new Test());
System.out.println("按名字排序后:");
for (Student s : list) {
System.out.println(s);
}
}
}
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:
public class Employee implements Comparable<Employee>{
//成员变量
private String id;
private String name;
private float salary;
//构造器
public Employee() {
super();
}
public Employee(String id, String name, float salary) {
super();
this.setId(id);
this.setName(name);
this.setSalary(salary);
}
//getters&setters
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 float getSalary() {
return salary;
}
public void setSalary(float salary) {
this.salary = salary;
}
//重写toString
@Override
public String toString() {
return "员工 [编号:" + getId() + ", 姓名:" + getName() + ", 工资:" + getSalary() + "]";
}
@Override
public int compareTo(Employee e) {
//工资降序
float s1 = this.getSalary();
float s2 = e.getSalary();
int n = new Float(s2-s1).intValue();
return n;
}
}
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
public class Test {
public static void main(String[] args) {
List<Employee> list = new ArrayList<>();
list.add(new Employee("emp001", "张三", 1800.0F));
list.add(new Employee("emp002", "李四", 2500.0F));
list.add(new Employee("emp003", "王五", 1600.0F));
System.out.println("排序前:");
for (Employee e : list) {
System.out.println(e);
}
Collections.sort(list);
System.out.println("排序后:");
for (Employee e : list) {
System.out.println(e);
}
}
}