HashMap的使用

来源：互联网发布：冯绍峰项羽知乎编辑：程序博客网时间：2024/05/07 02:41

package test;import java.util.HashMap;import java.util.Iterator;import java.util.Map;import java.util.Set;public class MapDemo2 {public static void main(String[] args) {// TODO 自动生成的方法存根HashMap<Student,String> hashMap = new HashMap<Student,String>();hashMap.put(new Student("zhangsan",21), "male");hashMap.put(new Student("lisi",22), "female");hashMap.put(new Student("wangwu",21), "male");hashMap.put(new Student("wangwu",21), "female");//使用entrySet方法同样可以对Map中元素进行迭代取出Set<Map.Entry<Student,String>> set = hashMap.entrySet();Iterator<Map.Entry<Student, String>> it = set.iterator();while(it.hasNext()){Map.Entry<Student, String> student = it.next();Student key = student.getKey();String value = student.getValue();System.out.println(key + ":" + value);}}}class Student implements Comparable<Student>{private String name;private int age;Student(String name,int age){this.name = name;this.age = age;}public String getName() {return name;}public int getAge() {return age;}@Overridepublic String toString() {return "Student [name=" + name + ", age=" + age + "]";}public int hashCode(){return name.hashCode() + age*3;}public boolean equals(Object obj){if(!(obj instanceof Student)){throw new ClassCastException();}Student stu = (Student) obj;return this.name.equals(stu.name) && this.age == stu.age;}@Overridepublic int compareTo(Student o) {int flag = new Integer(this.age).compareTo(new Integer(o.age));if(flag == 0){return this.name.compareTo(o.name);}else{return flag;}}}

输出结果为：

由于重写了hashCode和equals方法，HashMap保证了键的唯一性，所以当试图hashMap.put(new Student("wangwu",21), "female")，会替换该键的旧值，

最后输出Student [name=wangwu, age=21]:female