为什么自定义对象不是HashMap的等效键？

本文介绍了为什么自定义对象不是HashMap的等效键？的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述 29岁程序员，3月因学历无情被辞！ public class ActorId { private final int playerId; private final int id; ActorId（int playerId，int id）{ this.playerId = playerId; this.id = id; } public boolean equals（ActorId other）{ return this.id == other.id&&& this.playerId == other.playerId; } public int hashCode（）{ int hash = 1; hash = hash * 31 + playerId; hash = hash * 31 + id; 返回哈希; } public String toString（）{ return＃+ playerId +。 + id; } public int getPlayerId（）{ return playerId; } } 这是一个失败的JUnit测试 import static org.junit.Assert。*; import java.util.Map; import org.junit.Test; public class ActorIdTest { @Test public final void testAsMapKey（）{ ActorId a = new ActorId（123,345）; ActorId b = new ActorId（123,345）; assertTrue（a.equals（b））; assertEquals（a.hashCode（），b.hashCode（））; //使用字符串作为键映射< String，String> map1 = new java.util.HashMap< String，String>（）; map1.put（a.toString（），test）; assertEquals（test，map1.get（a.toString（）））; assertEquals（test，map1.get（b.toString（）））; assertEquals（1，map1.size（））; //但不是与ActorIds 映射< ActorId，String> map2 = new java.util.HashMap< ActorId，String>（）; map2.put（a，test）; assertEquals（test，map2.get（a））; assertEquals（test，map2.get（b））; // FAILS here assertEquals（1，map2.size（））; map2.put（b，test2）; assertEquals（1，map2.size（））; assertEquals（test2，map2.get（a））; assertEquals（test2，map2.get（b））; } } 解决方案你需要更改 public boolean equals（ActorId other）{ .... } 至 public boolean equals（Object other）{ .... } 提示：始终使用 @Override 注释。 如果您使用了 @Override 注释，编译器将会收到错误并说： 类型ActorId的方法equals（ActorId）必须覆盖或实现超类型方法 I'm having trouble using my own class as a key for a HashMap public class ActorId { private final int playerId; private final int id; ActorId(int playerId, int id) { this.playerId = playerId; this.id = id; } public boolean equals(ActorId other) { return this.id == other.id && this.playerId == other.playerId; } public int hashCode() { int hash = 1; hash = hash * 31 + playerId; hash = hash * 31 + id; return hash; } public String toString() { return "#" + playerId + "." + id; } public int getPlayerId() { return playerId; } }Here is a failing JUnit test import static org.junit.Assert.*; import java.util.Map; import org.junit.Test; public class ActorIdTest { @Test public final void testAsMapKey() { ActorId a = new ActorId(123, 345); ActorId b = new ActorId(123, 345); assertTrue(a.equals(b)); assertEquals(a.hashCode(), b.hashCode()); // Works with strings as keys Map<String, String> map1 = new java.util.HashMap<String, String>(); map1.put(a.toString(), "test"); assertEquals("test", map1.get(a.toString())); assertEquals("test", map1.get(b.toString())); assertEquals(1, map1.size()); // But not with ActorIds Map<ActorId, String> map2 = new java.util.HashMap<ActorId, String>(); map2.put(a, "test"); assertEquals("test", map2.get(a)); assertEquals("test", map2.get(b)); // FAILS here assertEquals(1, map2.size()); map2.put(b, "test2"); assertEquals(1, map2.size()); assertEquals("test2", map2.get(a)); assertEquals("test2", map2.get(b)); } } 解决方案 You need to changepublic boolean equals(ActorId other) { ....}to public boolean equals(Object other) { ....}Tip of the day: Always use @Override annotation.If you had used the @Override annotation, the compiler would have caught the error and said: The method equals(ActorId) of type ActorId must override or implement a supertype method 这篇关于为什么自定义对象不是HashMap的等效键？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！ 阿里云证书，YYDS！