java – 将对象作为参数传递,并在方法内进行修改

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假设我有一个Map< String,String>我想删除所有包含foo的值.在优化/内存等方面,最好的方法是什么?下面的四个syso打印相同的结果,也就是说{n2 = bar}. @H_301_2@public static void main(String[] args) { Map<String,String> in = new HashMap<String,String>(); in.put("n1","foo"); in.put("n2","bar"); in.put("n3","foobar"); // 1- create a new object with the returned Map Map<String,String> in1 = new HashMap<String,String>(in); Map<String,String> out1 = methodThatReturns(in1); System.out.println(out1); // 2- overwrite the initial Map with the returned one Map<String,String> in2 = new HashMap<String,String>(in); in2 = methodThatReturns(in2); System.out.println(in2); // 3- use the clear/putAll methods Map<String,String> in3 = new HashMap<String,String>(in); methodThatClearsAndReadds(in3); System.out.println(in3); // 4- use an iterator to remove elements Map<String,String> in4 = new HashMap<String,String>(in); methodThatRemoves(in4); System.out.println(in4); } public static Map<String,String> methodThatReturns(Map<String,String> in) { Map<String,String> out = new HashMap<String,String>(); for(Entry<String,String> entry : in.entrySet()) { if(!entry.getValue().contains("foo")) { out.put(entry.getKey(),entry.getValue()); } } return out; } public static void methodThatClearsAndReadds(Map<String,entry.getValue()); } } in.clear(); in.putAll(out); } public static void methodThatRemoves(Map<String,String> in) { for(Iterator<Entry<String,String>> it = in.entrySet().iterator(); it.hasNext();) { if(it.next().getValue().contains("foo")) { it.remove(); } } }

解决方法

最好的方法是methodThatRemoves因为:

>在内存消耗方面:它不会创建一个新的地图,所以不会增加内存开销.>在cpu使用方面:iterator具有O(1)复杂度,用于调用next或删除当前元素.

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