java中Map判断是否为空之isEmpty()与==null的区别
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Map map = new HashMap(); System.out.println("判断map是否有内容:"+map.isEmpty());//返回true System.out.println("判断map是否为null:"+map==null);//返回false Map map = new HashMa...
Map map = new HashMap
System.out.println("判断map是否有内容:"+map.isEmpty());//返回true
System.out.println("判断map是否为null:"+map==null);//返回false
Map map = new HashMap
map=null;
System.out.println("判断map是否为null:"+(map==null));//结果为true
System.out.println("判断map是否有内容:"+map.isEmpty());//NullPointerException
Map map = new HashMap
map.put(null,null);
System.out.println("判断map是否为null:"+(map==null));//false
System.out.println("判断map是否有内容:"+map.isEmpty());//false