WeakHashMap String键值探究

今天研究了一下WeakHashMap 出现了一个现象，使用String key1="key1"  与String key1=new String("key1") 结果大不相同，代码如下，还请大家帮忙分析一下：

import java.util.HashMap;
import java.util.Map;
import java.util.WeakHashMap;

public class TestWeakHashMap {
public static void main(String[] args) throws InterruptedException {
String key1 = new String("k1");
String key2 = new String("K2");
//String key1 = "k1";
//String key2 = "k2";
Map<String,String> map = new HashMap<String,String>();
Map<String,String> wmap = new WeakHashMap<String,String>();
map.put(key1, "val1");
map.put(key2, "val2");
wmap.put(key1, "wval1");
wmap.put(key2, "wval2");
map.remove(key2);
key2 = null;
key1 = null;
System.gc();
System.out.println("first  access: " + wmap.size());
System.out.println("second access: " + wmap.size());
System.out.println("map: " + map.toString());
System.out.println("wmap: " + wmap.toString());
}
}