Java 8, compare two maps and return result

Question

I am comparing 2 maps using Java 8 features and based on condition wants to return the result. Using .forEach is showing compile time error and basically, the return is returning from Lambda expression and not from the loop. How can I return from the loop enclosing the lambda?
Note that I am not comparing for equality for the two map objects

nMap.forEach((k,v) -> {
    if (!mMap.containsKey(k) || mMap.get(k) < v) {
        return -1;
    }
});

The `foreach` method accepted the `Comsumer`. It mean the void method. You can return in that. — Cường Lư Quốc, Oct 11 '18 at 07:15
forEach(..) has argument of type consumer. Consumer interface has abstract method ( void accept(...).. so inshort your lambda should not return any thing from there. — RAHUL ROY, Oct 11 '18 at 07:17
Possible duplicate of [Break or return from Java 8 stream forEach?](https://stackoverflow.com/questions/23308193/break-or-return-from-java-8-stream-foreach) — Lars, Oct 11 '18 at 07:18
Possible duplicate of [Comparing two maps](https://stackoverflow.com/questions/24814577/comparing-two-maps) — Jean-Baptiste Yunès, Oct 11 '18 at 07:29
`for (Map.Entry entry : nMap.entrySet()) { V value = mMap.get(entry.getKey()); if (value == null || value < entry.getValue()) { return -1; } }` — Hadi J, Oct 11 '18 at 07:32

Eran · Accepted Answer · 2018-10-11T08:08:07.780

8

Use a Stream of the entrySet() and anyMatch instead of forEach:

boolean found = 
    nMap.entrySet()
        .stream()
        .anyMatch(e -> !mMap.containsKey(e.getKey()) || mMap.get(e.getKey()) < e.getValue());
if (found)
    return -1;

edited Oct 11 '18 at 08:08

answered Oct 11 '18 at 07:14

Eran

387,369
54
702
768

I want to check if all entries in nMap matches the condition. – Abhinav Tyagi Oct 11 '18 at 07:38
2

@AbhinavTyagi In that case, why did you return -1 the first time your condition was true? Anyway, if you want to check all entries, change anyMatch to allMatch – Eran Oct 11 '18 at 07:39
1

If you're only using `e.getKey()` in the lambda body, you could just use `nMap.keySet().stream()` instead. (And are you missing a `< v`?) – Andy Turner Oct 11 '18 at 07:56
@AndyTurner yes, I must have accidentally deleted it when I formatted my answer. thanks – Eran Oct 11 '18 at 08:09
Alternatively: `boolean found = !mMap.keySet().containsAll(nMap.keySet()) || nMap.entrySet().stream() .anyMatch(e -> mMap.get(e.getKey()) < e.getValue());` – Holger Oct 11 '18 at 09:20

score 2 · Answer 2 · edited Oct 11 '18 at 12:57

2

Another approach using a Stream which filters the entries according to the given condition. The result of the streaming is an Optional which may contain a found Entry:

if (nMap.entrySet().stream()
        .filter(e -> !mMap.containsKey(e.getKey()) || mMap.get(e.getKey()) < e.getValue())
        .findAny()
        .isPresent()) {
    return -1;
}

edited Oct 11 '18 at 12:57

fps

33,623
8
55
110

answered Oct 11 '18 at 08:07

LuCio

5,055
2
18
34

1

@Federico Peralta Schaffner Thx for spotting this. – LuCio Oct 11 '18 at 12:59

Java 8, compare two maps and return result

2 Answers2