import java.util.HashMap;
import java.util.Map;
import java.util.Set;
public class HashMapTest {
public static void main(String[] args) {
// Integer是key,它的hashCode和equals都重写了
Map<Integer,String> map = new HashMap<>();
map.put(2,"eYuJun2");
map.put(3,"eYuJun3");
map.put(1,"eYuJun1");
map.put(3,"eYuJun3");// key重复,value会被覆盖
System.out.println(map.size());//3
// 遍历map集合
Set<Map.Entry<Integer,String>> set = map.entrySet();
for (Map.Entry<Integer,String> entry:set){
System.out.println(entry);
}
}
}
import java.util.*;
public class HashMapTest {
public static void main(String[] args) {
Student s1 = new Student("eYuJun1");
Student s2 = new Student("eYuJun2");
Student s3 = new Student("eYuJun3");
Student s4 = new Student("eYuJun3");
System.out.println(s4.equals(s3));
System.out.println("s3的hashCode:" + s3.hashCode());
System.out.println("s4的hashCode:" + s4.hashCode());
Set<Student> students = new HashSet<>();
students.add(s3);
students.add(s4);
System.out.println(students.size());
}
}
class Student{
private String name;
public Student() {
}
public Student(String name) {
this.name = name;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
Student student = (Student) o;
return Objects.equals(name, student.name);
}
@Override
public int hashCode() {
return Objects.hash(name);
}
}
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