1 package day7.lesson1.anli1;
2
3 import java.util.HashMap;
4 import java.util.Map;
5 import java.util.Set;
6
7 /*
8 1.5 Map集合的案例
9
10 1.5.1 案例-HashMap集合存储学生对象并遍历#1
11 创建一个HashMap集合，键是学号(String)，值是学生对象(Student)。存储三个键值对元素，并遍历
12 */
13 public class HashMapDemo {
14 public static void main(String[] args) {
15 HashMap<String, Student> map = new HashMap<>();
16
17 Student s1 = new Student("zhangsan" , 12);
18 Student s2 = new Student("lisi" , 14);
19 Student s3 = new Student("wangwu" , 12);
20
21 map.put("itheima01", s1);
22 map.put("itheima02", s2);
23 map.put("itheima03", s3);
24
25 Set<String> keySet = map.keySet();
26 for (String id: keySet){
27 Student stu = map.get(id);
28 System.out.println("学号：" + id + ", 姓名：" + stu.getName() + "， 年龄：" + stu.getAge());
29 }
30 /*
31 学号：itheima01, 姓名：zhangsan， 年龄：12
32 学号：itheima02, 姓名：lisi， 年龄：14
33 学号：itheima03, 姓名：wangwu， 年龄：12
34 */
35
36 System.out.println();
37 Set<Map.Entry<String, Student>> entrySet = map.entrySet();
38 for (Map.Entry<String, Student> me: entrySet){
39 String id = me.getKey();
40 Student stu = me.getValue();
41 System.out.println("学号：" + id + ", 姓名：" + stu.getName() + "， 年龄：" + stu.getAge());
42 }
43 }
44 }
1 package day7.lesson1.anli1;
2
3 public class Student {
4
5 private String name;
6 private int age;
7
8 public Student() {
9 }
10
11 public Student(String name, int age) {
12 this.name = name;
13 this.age = age;
14 }
15
16 public void setName(String name) {
17 this.name = name;
18 }
19
20 public void setAge(int age) {
21 this.age = age;
22 }
23
24 public String getName() {
25 return name;
26 }
27
28 public int getAge() {
29 return age;
30 }
31 }
1 package day7.lesson1.anli2;
2
3 import java.util.HashMap;
4 import java.util.Map;
5 import java.util.Set;
6
7 /*
8 1.5.2 案例-HashMap集合存储学生对象并遍历#2
9 创建一个HashMap集合，键是学生对象(Student)，值是居住地 (String)。存储多个元素，并遍历。
10 要求保证键的唯一性：如果学生对象的成员变量值相同，我们就认为是同一个对象
11 学生类中重写hashCode() & equels()
12 */
13 public class HashMapDemo {
14 public static void main(String[] args) {
15 HashMap<Student, String> hm = new HashMap<>();
16
17 Student s1 = new Student("zhangsan", 12);
18 Student s2 = new Student("lisi", 14);
19 Student s3 = new Student("wangwu", 12);
20 Student s4 = new Student("wangwu", 12);
21
22 hm.put(s1, "北京");
23 hm.put(s2, "上海");
24 hm.put(s3, "南京");
25 hm.put(s4, "武汉");
26
27 Set<Student> keySet = hm.keySet();
28 for (Student student: keySet){
29 String address = hm.get(student);
30 System.out.println("姓名：" + student.getName() + ", 年龄：" + student.getAge() + ", 地址：" + address);
31 }
32 /*
33 //学生类中重写hashCode() & equels()之前：
34 姓名：lisi, 年龄：14, 地址：上海
35 姓名：wangwu, 年龄：12, 地址：武汉
36 姓名：zhangsan, 年龄：12, 地址：北京
37 姓名：wangwu, 年龄：12, 地址：南京
38
39 //学生类中重写hashCode() & equels()之后：
40 姓名：zhangsan, 年龄：12, 地址：北京
41 姓名：wangwu, 年龄：12, 地址：武汉 //值（address）被覆盖了
42 姓名：lisi, 年龄：14, 地址：上海
43 */
44
45 System.out.println();
46 Set<Map.Entry<Student, String>> entrySet = hm.entrySet();
47 for (Map.Entry<Student, String> me: entrySet){
48 Student student = me.getKey();
49 String address = me.getValue();
50 System.out.println("姓名：" + student.getName() + ", 年龄：" + student.getAge() + ", 地址：" + address);
51 }
52 }
53 }
1 package day7.lesson1.anli2;
2
3 public class Student {
4
5 private String name;
6 private int age;
7
8 public Student() {
9 }
10
11 public Student(String name, int age) {
12 this.name = name;
13 this.age = age;
14 }
15
16 public void setName(String name) {
17 this.name = name;
18 }
19
20 public void setAge(int age) {
21 this.age = age;
22 }
23
24 public String getName() {
25 return name;
26 }
27
28 public int getAge() {
29 return age;
30 }
31
32 @Override
33 public boolean equals(Object o) {
34 if (this == o) return true;
35 if (o == null || getClass() != o.getClass()) return false;
36
37 Student student = (Student) o;
38
39 if (age != student.age) return false;
40 return name != null ? name.equals(student.name) : student.name == null;
41 }
42
43 @Override
44 public int hashCode() {
45 int result = name != null ? name.hashCode() : 0;
46 result = 31 * result + age;
47 return result;
48 }
49 }
