java:集合框架(HashMap集合键是Student值是String的案例)

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因为键值是Student对象，所以每个对象的引用地址都是不同的，如果Student类不重写hashcode和equals方法的话，就会全部写进去。

测试类：

import java.util.HashMap;

import com.heima.bean.Student;

public class Demo5_HashMap {

	public static void main(String[] args) {
		HashMap<Student, String> hs=new HashMap<>();
		hs.put(new Student("张三",23),"北京");
		hs.put(new Student("张三",23),"上海");
		hs.put(new Student("李四",24),"广州");
		hs.put(new Student("王五",25),"深圳");
		System.out.println(hs);
	}

}

运行结果：

{Student [name=张三, age=23]=上海, Student [name=李四, age=24]=广州, Student [name=王五, age=25]=深圳}

Student类：

public class Student {
	private String name;
	private int age;
	public Student() {
		super();
		
	}
	public Student(String name, int age) {
		super();
		this.name = name;
		this.age = age;
	}
	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;
	}
	@Override
	public String toString() {
		return "Student [name=" + name + ", age=" + age + "]";
	}
	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + age;
		result = prime * result + ((name == null) ? 0 : name.hashCode());
		return result;
	}
	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		Student other = (Student) obj;
		if (age != other.age)
			return false;
		if (name == null) {
			if (other.name != null)
				return false;
		} else if (!name.equals(other.name))
			return false;
		return true;
	}
	
}