Can anyone explain why this works in java 7 and not java 6?

Question

I'm using this code:

public static void printMap(Map<Integer, String> obj) {
        for (Map.Entry e : obj.entrySet()) {
            if (e.getKey() == 3) {
                System.out.println("OK!");
            }
        }
    }

and it works in Java 7. But in Java 6 it gives an error on the line:

if (e.getKey() == 3) {

Can anyone explain to me why I get this error?

In an earlier version I'd say it's an autoboxing problem. But Java 6 does support autoboxing. Are you sure it's actually Java 6? — DerMike, Mar 05 '13 at 17:31
It's because you can't == an object to a primitive. Java7 understands it is an Integer and will auto-unbox it, but Java6 will need you to parametrise the `Entry`. — entonio, Mar 05 '13 at 17:32
You are not using Generic type while getting Map.Entry .. It should be `Map.Entry e` for version before java version before below 7 — Vishal K, Mar 05 '13 at 17:33
The e.getKey return object and compared with 3 without type cast! This works in java 7, but in 6 it give error! — Ascension, Mar 05 '13 at 17:34

score 2 · Accepted Answer · answered Mar 05 '13 at 17:32

2

In java 6, you need to specify the types for your Map.Entry variable

Map.Entry<Integer, String> e : obj.entrySet()

before you compare the key or value of such an Entry. Otherwise the compiler thinks you are doing

if (<object of type Object> == 3)

which makes no sense to it.

answered Mar 05 '13 at 17:32

Sotirios Delimanolis

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So, this is new resource of Java 7, is not? – Ascension Mar 05 '13 at 17:40
Yes, you can look at [type inference](http://docs.oracle.com/javase/tutorial/java/generics/genTypeInference.html) for more information. – Sotirios Delimanolis Mar 05 '13 at 17:42

score 1 · Answer 2 · answered Mar 05 '13 at 17:32

Presumably you need to assign a type to your Entry:

public static void printMap(Map<Integer, String> obj) {
    for (Map.Entry<Integer, String> e : obj.entrySet()) {
        if (e.getKey() == 3) {
            System.out.println("OK!");
        }
    }
}

There are changes in Java 7 to the generics framework. I am not sure whether that code would, as you suggest, work in Java 7 but I can say that you need to specify the generic types of Entry for it to work in Java 6.

score 0 · Answer 3 · answered Mar 05 '13 at 17:35

Its a template problem in Java 6 I think.

This fixes it:

public static void printMap(Map obj) {

    for (Map.Entry<Integer, String> e : obj.entrySet()) {
        if (e.getKey() == 3) {
            System.out.println("OK!");
        }
    }
}

Java 6 doesn't auto pass the arguments from the Map to the Map.Entry

score -2 · Answer 4 · answered Mar 05 '13 at 17:34

-2

Try this

if (e.getKey().toString().equals("3"))

I think e.getKey() returns an object and you were comparing it with integer. Either convert it to integer and compare or to String and compare

answered Mar 05 '13 at 17:34

codingbiz

26,179
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The method is `toString()` and you don't use `==` operator to compare strings in Java. – Sotirios Delimanolis Mar 05 '13 at 17:35
This would fix the problem but it is not the underlying issue. – Boris the Spider Mar 05 '13 at 17:36
too much mistakes in one short line :/ – A4L Mar 05 '13 at 17:36

Can anyone explain why this works in java 7 and not java 6?

4 Answers4