Java ArrayList contains details.

最新推荐文章于 2021-08-07 19:21:04 发布

原创最新推荐文章于 2021-08-07 19:21:04 发布 · 590 阅读

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本文介绍了一个简单的Java程序，通过定义Apple类来演示如何覆盖hashCode()和equals()方法，确保对象能正确地在集合中进行比较与检索。主测试类MainTest展示了如何使用这些方法检查List集合中是否存在特定的Apple对象。

Apple.java

package com.jue.test;

public class Apple {

	int id;
	String name;

	public Apple(int newid, String newname) {
		id = newid;
		name = newname;
	}

	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + id;
		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;
		Apple other = (Apple) obj;
		if (id != other.id)
			return false;
		if (name == null) {
			if (other.name != null)
				return false;
		} else if (!name.equals(other.name))
			return false;
		return true;
	}

}

MainTest.java

package com.jue.test;

import java.util.ArrayList;
import java.util.List;

public class MainTest {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		List<Apple> lists = new ArrayList<Apple>();
		lists.add(new Apple(1, "a"));
		lists.add(new Apple(2, "b"));
		lists.add(new Apple(3, "c"));

		System.out.print(lists.contains(new Apple(1, "a")));
	}

}

result:

true.