CODEWITHSUNDEEP
javalambdajava-8
AbNig
AbNig

Reputation: 352

Lambda Expression to find sum

I have a class as below:

public class Class2 {

private final Integer x;

private final Integer y;

public Class2(final Integer x, Integer y) {
    this.x = x;
    this.y = y;
}

public Integer getX() {
    return x;
}

public Integer getY() {
    return y;
}

}

I have a Map object like below:

Map<MyEnum , List<Class2>> mapX

I want to find the sum of x & y members of the Class2 instances in the List instance which is the value item in the above map. I want to use lambda expressions

I have come up with the following incomplete lambda. Thanks in advance.

        mapX.entrySet().forEach(entry -> {
            System.out.println("MapX-Key : " + entry.getKey() + "\nMapX-Value : "
                    + entry.getValue().stream().collect(Collectors.summingInt(???)));
        });

Upvotes: 2

Views: 2106

Answers (2)

OldCurmudgeon
OldCurmudgeon

Reputation: 65889

Not quite sure about what you're asking but one of these should help:

// Using Class2
Map<MyEnum , List<Class2>> mapX = null;
mapX.entrySet().forEach(entry -> {
        System.out.println("MapX-Key : " + entry.getKey() + "\nMapX-Value : "
                + entry.getValue().stream()
                .collect(Collectors.summingInt(x -> x.getX() + x.getY())));
});

// Values from Class2 via Class1
Map<MyEnum , List<Class1>> map1 = null;
map1.entrySet().forEach(entry -> {
        System.out.println("MapX-Key : " + entry.getKey() + "\nMapX-Value : "
                + entry.getValue().stream()
                .collect(Collectors.summingInt(x -> x.getClass2().getX() + x.getClass2().getY())));
});

Upvotes: 2

azro
azro

Reputation: 54168

You can go this way : 

mapX.entrySet().stream()
               .map(entry -> "MapX-Key : " + entry.getKey() 
                           + "\nMapX-Value : " 
                           + entry.getValue().stream().mapToInt(e -> e.getX() + e.getY()))
               .forEach(System.out::println);

This will iterate over each Entry, then (map) create a String with the key, and then the sum of x and y, and at the end print them

Upvotes: 2

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