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HashMap<String,String> map = new HashMap<>(); map.put("Name", "June"); map.put("QQ", "2572073701"); String a = map.get("name"); boolean flag = "June".equals(map.get("name"));
a 为null
map中取没有的key,会得到value为null,flag为false,不会报错
HashMap<String,String> map = new HashMap<>(); map.put("Name", "June"); map.put("QQ", "2572073701"); boolean flag = "June".equals(map.get("Name"));
flag 为true
HashMap<String,String> map = new HashMap<>(); map.put("Name", "June"); map.put("QQ", "2572073701"); boolean flag = "June".equals(null);
flag为false,不会报错
需要学习javadoc看get方法,string的equals方法可以点进去看看