Java HashMap冲突实例
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看到这篇帖子，其实数据结构真实的存在于身边。模仿上文，弄个Java版的。
1、重写hashcode，最好（一定）要重写equals。即hashcode相同则equals返回true?
import java.util.HashMap;public class TestWorstHashMap {private static final int testSize = 100000;private static final int specialId = 1;private static final String specialName = "1";/************************************ test1 **************************************/class BadModel {private int id;private String name;public BadModel(int id, String name) {this.id = id;this.name = name;}/** * @see java.util.HashMap.put(K, V) */@Overridepublic boolean equals(Object obj) {if (obj instanceof BadModel) {return id == ((BadModel) obj).id && name.equals(((BadModel) obj).name);}return false;}@Overridepublic int hashCode() {return id;}}void testBadModel1() {HashMap<BadModel, Object> map = new HashMap<BadModel, Object>();long start = System.currentTimeMillis();for (int i = 0; i < testSize; i++) {BadModel model = new BadModel(specialId, "Name" + i);map.put(model, "test" + i);}long end = System.currentTimeMillis();System.out.println("BadModel the same id : " + (end - start));}void testBadModel2() {HashMap<BadModel, Object> map = new HashMap<BadModel, Object>();long start = System.currentTimeMillis();for (int i = 0; i < testSize; i++) {BadModel model = new BadModel(specialId, specialName);map.put(model, "test" + i);}long end = System.currentTimeMillis();System.out.println("BadModel the same id & name : " + (end - start));}/************************************ test2 **************************************/class GoodModel {private int id;private String name;public GoodModel(int id, String name) {this.id = id;this.name = name;}@Overridepublic boolean equals(Object obj) {if (obj instanceof GoodModel) {return id == ((GoodModel) obj).id && name.equals(((GoodModel) obj).name);}return false;}@Overridepublic int hashCode() {return id + name.hashCode();}}void testGoodModel() {HashMap<GoodModel, Object> map = new HashMap<GoodModel, Object>();long start = System.currentTimeMillis();for (int i = 0; i < testSize; i++) {GoodModel model = new GoodModel(specialId, "Name" + i);map.put(model, "test" + i);}long end = System.currentTimeMillis();System.out.println("GoodModel the same id : " + (end - start));}public static void main(String[] args) {TestWorstHashMap test = new TestWorstHashMap();test.testBadModel1();test.testBadModel2();test.testGoodModel();}}??
测试结果：
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BadModel the same id ?: 141454
BadModel the same id & name : 28
GoodModel the same id ?: 92
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