Setting Default Values in HashMap

Question

I am trying to find a way to make a HashMap return a default value. For example if you look at the following this will printout "Test:=null" what if I want to request a default value so anytime I try to get something that is NOT set in the hashMap I will get the value?

Map<String, String> test = new HashMap<String, String>();
test.put("today","monday");
System.out.println("Test =:" + test.get("hello") + "");

Override the `Map`. Note this will break the contract. – Boris the Spider Jun 20 '13 at 18:17 — Boris the Spider, Jun 20 '13 at 18:17

score 8 · Answer 1 · edited Jun 20 '13 at 18:26

8

Try the following:

Map<String,String> map = new HashMap<String,String>(){
    @Override
    public String get(Object key) {
        if(! containsKey(key))
            return "DEFAULT";
        return super.get(key);
    }
};

System.out.println(map.get("someKey"));

edited Jun 20 '13 at 18:26

blackpanther

10,998
11
48
78

answered Jun 20 '13 at 18:17

Arno Mittelbach

952
5
12

score 4 · Accepted Answer · answered Jun 20 '13 at 18:21

Better check the return value instead of changing the way a Map works IMO. The Commons Lang StringUtils.defaultString(String) method should do the trick:

Map<String, String> test = new HashMap<>();
assertEquals("", StringUtils.defaultString(test.get("hello")));
assertEquals("DEFAULT", StringUtils.defaultString(test.get("hello"), "DEFAULT"));

StringUtils JavaDoc is here.

score 2 · Answer 3 · answered Jun 20 '13 at 18:18

2

Rather than try to give a value to the data, why don't you just do a check when you want to pull the data?

if (!set.containsKey(key)){
    return default_value;
}
else{
    return set.get(key);
}

answered Jun 20 '13 at 18:18

Daniel

2,435
5
26
40

Visruth · Answer 4 · 2015-05-02T12:12:47.167

No, you can't use it as a switch condition. You can override the get method by extending it into another class or you may try it as follows :

Map<String, String> test = new HashMap<String, String>();
test.put("today", "monday");
String s = test.get("hello") == null? "default value" : test.get("hello");
System.out.println("Test =:" + s);

or

    final String defaultValue = "default value";
    Map<String, String> test = new HashMap<String, String>() {

        @Override
        public String get(Object key) {
            String value = super.get(key);
            if (value == null) {
                return defaultValue;
            }
            return value;
        };
    };
    test.put("today", "monday");            
    System.out.println("Test =:" + test.get("nokey"));

And also you can achieve this by simply using Properties class instead of HashMap.

        Properties properties = new Properties();
        properties.setProperty("key1", "value of key1");
        String property1 = properties.getProperty("key1", "default value");
        String property2 = properties.getProperty("key2", "default value");
        System.out.println(property1);
        System.out.println(property2);

which prints :

value of key1
default value

score 0 · Answer 5 · answered Jun 20 '13 at 18:18

0

Extend the HashMap and override the get().

answered Jun 20 '13 at 18:18

AllTooSir

48,828
16
130
164

Setting Default Values in HashMap

5 Answers5

Linked