Difference between two hashmaps and overwrite value on match-CodePudding

Im relativly new to Java and i ran into some problems. The goal is to compare the parameters, e.g. -DmyCustomArg="my_value", i specify in the jvm with the map and overwrite the matching key with new value.

So i have two hashmaps, one is the System.getProperties() and the other is a map with parameters. Now I want to compare both and replace matching values.

I have already tried

  Map properties = System.getProperties();
  Map<String, String> parameter = new HashMap<>();

  parameter.put("1", "value one");
  parameter.put("2", "value two");
  parameter.put("myCustomArg", "value three");

    for (int i = 0; i < parameter.keySet().toArray().length; i  ) {
        if (properties.containsKey(parameter.keySet().toArray()[i])) {
            parameter.replace(properties.get( ??? ))
        }
    }

But now I can't get any further. How do I get to the value where it matched so I can replace it? Do I have to create a third map where the results are stored or is there an easier way?

CodePudding user response：

welcome,

You can use this forEach loop:

        Properties properties = System.getProperties();
        Map<String, String> map = new HashMap<>();

        map.put("1", "value one");
        map.put("2", "value two");
        map.put("myCustomArg", "value three");

        map.forEach((key, value)->{
            if(properties.containsKey(key)){
                System.setProperty(key, value);
            }
        });

or if you'd like to loop the entry set without lambda, you can replace the map.forEach() with this:

        for (Map.Entry<String, String> entry : map.entrySet()) {
            String key = entry.getKey();
            String value = entry.getValue();
            if(properties.containsKey(key)){
                System.setProperty(key, value);
            }
        }

or if you'd like to loop the keys only:

        for (String key : map.keySet()) {
            if(properties.containsKey(key)){
                System.setProperty(key, map.get(key));
            }
        }

CodePudding user response：

If you need to override the properties is enough to use the same key value in the map. Map will replace previous value.

E.g:

Map systemProperties = System.getProperties();

System.out.println("java.runtime.version before: "   systemProperties.get("java.runtime.version"));

systemProperties.put("java.runtime.version", "17.0.0");

// Print the new value
System.out.println("java.runtime.version after: "   systemProperties.get("java.runtime.version"));