我知道HashSet
基于HashMap
实现,但是它用于需要唯一元素的集合。那么为什么在下面的代码中,当将相同的对象放入映射和集合时,两个集合的大小都等于1?难道映射大小不应该是2吗?因为如果两个集合的大小相等,我看不出使用这两个集合有任何区别。
Set testSet = new HashSet<SimpleObject>();
Map testMap = new HashMap<Integer, SimpleObject>();
SimpleObject simpleObject1 = new SimpleObject("Igor", 1);
SimpleObject simplObject2 = new SimpleObject("Igor", 1);
testSet.add(simpleObject1);
testSet.add(simplObject2);
Integer key = new Integer(10);
testMap.put(key, simpleObject1);
testMap.put(key, simplObject2);
System.out.println(testSet.size());
System.out.println(testMap.size());
输出结果为 1 和 1。
SimpleObject code
public class SimpleObject {
private String dataField1;
private int dataField2;
public SimpleObject(){}
public SimpleObject(String data1, int data2){
this.dataField1 = data1;
this.dataField2 = data2;
}
public String getDataField1() {
return dataField1;
}
public int getDataField2() {
return dataField2;
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result
+ ((dataField1 == null) ? 0 : dataField1.hashCode());
result = prime * result + dataField2;
return result;
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
SimpleObject other = (SimpleObject) obj;
if (dataField1 == null) {
if (other.dataField1 != null)
return false;
} else if (!dataField1.equals(other.dataField1))
return false;
if (dataField2 != other.dataField2)
return false;
return true;
}
}