1.java.util.HashMap 的 clone 方法是浅层copy，clone出来的对象，仅仅是原来对象的一个引用，并且对克隆出来的对象进行操作是无效的。
下面是个例子：importjava.util.HashMap;importjava.util.Iterator;importjava.util.Map;/***@authorhzp
**/
public classTest {/***@paramargs*/
public static voidmain(String[] args) {//TODO Auto-generated method stub
HashMap source= newHashMap();
source.put("key1","value1");
source.put("key2","value2");for(Iterator keyItr =source.keySet().iterator();keyItr.hasNext();) {
Object key=keyItr.next();
System.out.println(key+ " : "+source.get(key));
}
System.out.println("----------------- 1 ----------------");
Map targetMap=(HashMap)source.clone();for(Iterator keyItr =targetMap.keySet().iterator();keyItr.hasNext();){
Object key=keyItr.next();
System.out.println(key+ " : "+source.get(key));
}
System.out.println("---------------- 2 ----------------");
Object temp= targetMap.put("key1","modify");
System.out.println("temp : "+temp);for(Iterator keyItr =source.keySet().iterator();keyItr.hasNext();){
Object key=keyItr.next();
System.out.println(key+ " : "+source.get(key));
}
}
}
输出结果为：
key1 : value1
key2 : value2----------------- 1 ----------------key1 : value1
key2 : value2---------------- 2 ----------------temp : value1
key1 : value1
key2 : value2
若想实现深层copy，则需要自己重写clone方法。
如下面的例子：importjava.util.HashMap;importjava.util.Iterator;importjava.util.Map;/***@authorhzp
**/
public classTest {class customHashMap extendsHashMap {publiccustomHashMap() {super();
}public customHashMap(intinitialCapacity) {super(initialCapacity);
}publicObject clone() {
Map target= newHashMap();for (Iterator keyIt = this.keySet().iterator(); keyIt.hasNext();) {
Object key=keyIt.next();
target.put(key,this.get(key));
}returntarget;
}
}/***@paramargs*/
public static voidmain(String[] args) {//TODO Auto-generated method stub
customHashMap source= (new Test()).newcustomHashMap();
source.put("key1", "value1");
source.put("key2", "value2");for (Iterator keyItr =source.keySet().iterator(); keyItr.hasNext();) {
Object key=keyItr.next();
System.out.println(key+ " : " +source.get(key));
}
System.out.println("----------------- 1 ----------------");
Map target=(Map) source.clone();
target.put("key1", "modify");
System.out.println("----------------- 2 the souce map print----------------");for (Iterator keyItr =source.keySet().iterator(); keyItr.hasNext();) {
Object key=keyItr.next();
System.out.println(key+ " : " +source.get(key));
}
System.out.println("----------------- 3 the target map print----------------");for (Iterator keyItr =target.keySet().iterator(); keyItr.hasNext();) {
Object key=keyItr.next();
System.out.println(key+ " : " +target.get(key));
}
}
}
输出结果：
key1 : value1
key2 : value2----------------- 1 ----------------
----------------- 2 the souce map ----------------key1 : value1
key2 : value2----------------- 3 the target map ----------------key1 : modify
key2 : value2