6.2 HashSet和TreeSet
系列 - JAVA集合
目录
本实验手册主要内容是HashSet、LinkedHashSet和TreeSet
任务一：HashSet
Step 1 存储基本类型
import java.util.HashSet;
public class Example08 {
public static void main(String[] args) {
HashSet<String> names = new HashSet<>();
names.add("张三");
names.add("李四");
names.add("王五");
names.add("李四");
System.out.println(names);
}
}Step 2 存储自定义类型
import java.util.HashSet;
class Student {
String id;
String name;
public Student(String id, String name) {
this.id = id;
this.name = name;
}
public String toString() {
return id + ":" + name;
}
}
public class Example08 {
public static void main(String[] args) {
HashSet<Student> students = new HashSet<>();
Student s1 = new Student("1", "张三");
Student s2 = new Student("2", "李四");
Student s3 = new Student("2", "李四");
Student s4 = new Student("3", "王五");
students.add(s1);
students.add(s2);
students.add(s3);
students.add(s4);
System.out.println(students);
}
}修改后：
import java.util.HashSet;
class Student {
String id;
String name;
public Student(String id, String name) {
this.id = id;
this.name = name;
}
public String toString() {
return id + ":" + name;
}
public int hashCode() {
return id.hashCode();
}
// 判断自己和obj是不是相等
public boolean equals(Object obj) {
// 如果obj就是自己
if (this == obj) {
return true;
}
// 如果 obj 不是 Student 类型
if (!(obj instanceof Student)) {
return false;
}
// 把 obj 转换成 Student（强制类型转换）
Student other = (Student) obj;
// 我们认为学号相等就是同一个学生
return this.id.equals(other.id);
}
}
// 其他地方不变运行结果：
任务二：LinkedHashSet
把刚才代码中的 HashSet 改成 LinkedHashSet
任务三：TreeSet
Step 1 观察自动排序
import java.util.TreeSet;
public class Example11 {
public static void main(String[] args) {
TreeSet ts = new TreeSet();
ts.add(3);
ts.add(1);
ts.add(1);
ts.add(2);
ts.add(3);
System.out.println(ts);
}
}运行结果：
Step 2 存储自定义类型
import java.util.TreeSet;
public class Example12 {
public static void main(String[] args) {
Student s1 = new Student("1", "张三");
s1.setOrder(4);
Student s2 = new Student("2", "李四");
s2.setOrder(3);
Student s4 = new Student("3", "王五");
s4.setOrder(1);
TreeSet<Student> students = new TreeSet<>();
students.add(s1);
students.add(s2);
students.add(s4);
System.out.println(students);
}
}Step 3 实现Comparable接口
class Student implements Comparable<Student> {
String id;
String name;
int height; // 身高
public Student(String id, String name) {
this.id = id;
this.name = name;
}
public void setHeight(int height) {
this.height = height;
}
public String toString() {
return id + ":" + name;
}
public int hashCode() {
return id.hashCode();
}
public boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (!(obj instanceof Student)) {
return false;
}
Student other = (Student) obj;
return this.id.equals(other.id);
}
public int compareTo(Student other) {
if (this.height > other.height) {
return 1; // 返回正数：表示"我"比"你"大
} else if (this.height < other.height) {
return -1; // 返回负数：表示"我"比"你"小
} else {
return 0; // 返回0：表示"我"和"你"一样大
}
}
}import java.util.TreeSet;
public class Example12 {
public static void main(String[] args) {
Student s1 = new Student("1", "张三");
s1.setHeight(175);
Student s2 = new Student("2", "李四");
s2.setHeight(170);
Student s4 = new Student("3", "王五");
s4.setHeight(180);
TreeSet<Student> students = new TreeSet<>();
students.add(s1);
students.add(s2);
students.add(s4);
System.out.println(students);
}
}运行结果：
