Java : The Map value comparison is failing to compare with the higher values. Why?

Question

Why I'm getting only the message "a value is same" as an output ? Is it due to some auto-boxing ?

Code :

 Map<Character, Integer> pMap = new HashMap<>();
    Map<Character, Integer> sMap = new HashMap<>();
    char c = 'a';
    pMap.put(c, 10);
    sMap.put(c, 10);
    if (sMap.get(c) == pMap.get(c)) {
        System.out.println(c + " value is same");
    }
    char d = 'b';
    pMap.put(d, 10000);
    sMap.put(d, 10000);
    if (sMap.get(d) == pMap.get(d)) {
        System.out.println(d + " value is same");
    }

It's because Java caches the Integer instances from -127 to 128 — raviraja, Sep 20 '19 at 04:33
All java wrapper classes have `equals()` method implemented in it. So if you want to compare `Integer` object then always use `equals` method. — Sudhir Ojha, Sep 20 '19 at 04:35
Refer to this link for the answer : https://stackoverflow.com/questions/4428774/why-java-does-not-see-that-integers-are-equal — Anish B., Sep 20 '19 at 04:45

score 3 · Accepted Answer · answered Sep 20 '19 at 04:41

3

Integers are object types so for comparing them you should use Integer::equals. For Integers in range [-128 , 127] there is a special Integer pool. When you put your int values in the map, they are boxed to Integer - hence same values in your map, between [-128 , 127], will be references to same values in Integer pool. That is why == for [-128 , 127] values returns true. But generally you should use equals here or perform unboxing explicitly.

answered Sep 20 '19 at 04:41

Michał Krzywański

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Use `equals` or enforce `int` comparison, e.g. `sMap.get(d) == (int)pMap.get(d)`. – Holger Sep 20 '19 at 08:17

Java : The Map value comparison is failing to compare with the higher values. Why?

1 Answers1