HashSet的contains方法de解释是不是有问题
first of all, exhibits the code:
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import java.util.ArrayList;import java.util.HashSet;import java.util.Iterator;public class Test {int value;Test(int value) {this.value = value;}public boolean equals(Object obj) {if (obj instanceof Test) {Test foo = (Test) obj;return value == foo.value;} else {return false;}}public static void main(String[] args) {ArrayList list = new ArrayList();HashSet set = new HashSet();list.add(new Test(1));set.add(new Test(1));Iterator i = set.iterator();while (i.hasNext()) {Test temp = (Test) i.next();System.out.println(temp.equals(new Test(1)));}System.out.println(list.contains(new Test(1)) + ","+ set.contains(new Test(1)));System.out.println(new Test(1).equals(new Test(1)) + ","+ set.contains(new Test(1)));}}?
about contains, why list is true while set is false?
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my answer:
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HashSet与ArrayList的contains算法多加入了hashCode的考量
看源码，HashSet的contains方法最终是通过HashMap中的：
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/** * Returns the entry associated with the specified key in the * HashMap. Returns null if the HashMap contains no mapping * for the key. */final Entry <K,V> getEntry(Object key) { int hash = (key == null) ? 0 : hash(key.hashCode()); for (Entry <K,V> e = table[indexFor(hash, table.length)]; e != null; e = e.next) { Object k; if (e.hash == hash && ((k = e.key) == key || (key != null && key.equals(k)))) return e; } return null;} ?可见，hash和equals方法都是介入因素
但这里奇怪ArrayList和HashSet的contains方法javadoc一模一样，分别是:
Returns true if this list contains the specified element. More formally, returns true if and only if this list contains at least one element e such that (o==null ? e==null : o.equals(e)).
Returns true if this set contains the specified element. More formally, returns true if and only if this set contains an element e such that (o==null ? e==null : o.equals(e)).
开始真是迷惑了一下，若我没考虑错的话，HashSet的解释是否是漏写了hash的相关
若要相同，是否在Test类中再重写hashCode如：
public int hashCode() { return value;}??