public class Person{
	private String name;
	private int age;
｝

setter和getter方法已省略

測試類中：

HashSet<Person> hs = new HashSet<>();
hs.add(new Person("a",1));
hs.add(new Person("a",1));
hs.add(new Person("b",2));
hs.add(new Person("c",3));

重寫了hashCode()方法就可以執行Person中重寫的equals()方法。

Person類中重寫兩個方法（ME自動自成 ）

@Override
	public int hashCode() {
		/**
		 * final int prime = 31;
		 * 1,31是一個質數
		 * 2，31不大不小
		 * 3，2^5 - 1 = 31
		 */
		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;
		Person other = (Person) 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;
	}