Java – pass the object as a parameter and modify it within the method

Suppose I have a map < string, string > I want to delete all the values containing foo What is the best way to optimize / memory? The following four sysos print the same result, that is, {N2 = bar}

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);
    Sy@R_301_2354@.out.println(out1);

    // 2- overwrite the initial Map with the returned one 
    Map<String,String> in2 = new HashMap<String,String>(in);
    in2 = methodThatReturns(in2);
    Sy@R_301_2354@.out.println(in2);

    // 3- use the clear/putAll methods
    Map<String,String> in3 = new HashMap<String,String>(in);
    methodThatClearsAndReadds(in3);
    Sy@R_301_2354@.out.println(in3);

    // 4- use an iterator to remove elements
    Map<String,String> in4 = new HashMap<String,String>(in);
    methodThatRemoves(in4);
    Sy@R_301_2354@.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();
        }
    }
}

Solution

The best method is methodthatremoves because:

>In terms of memory consumption: it will not create a new map, so it will not increase memory overhead. > In terms of CPU usage: iterator has o (1) complexity, which is used to call next or delete the current element