How to find the sumOfelements in array of datatype

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I have a custom class

class StackInfo {
    int start, size, capacity;
}

and to verify the total number of elements present in an array of such info I have 

private int numberOfElements(StackInfo[] info) {
    int size = 0;
    for (StackInfo si : info) {
        size += si.size;
    }
    return size;
}

I tried converting it using streams to the following:

private int numberOfElements(StackInfo[] info) {
    return (int) Arrays.stream(info).map(s -> s.size).count();
    //       ^^ 
    //     to convert long
}

But the output for the above code is not correct either after casting as well.

java-stream java-8 arrays java
2 Answers

You seem to be looking for the sum operation and not count which would need you to convert the Stream to IntStream mostly. You can update your code to :

private int numberOfElementsStream(StackInfo[] info) {
    return Arrays.stream(info)    // Stream<StackInfo>
            .mapToInt(sd -> sd.size)   //IntStream of their size
            .sum();   // sum of all
}
user_17461180

You can use reduce operation:

Arrays.stream(info).reduce((s1, s2) -> s1.size + s2.size);

Or the sum as @nullpointer has shown :

Arrays.stream(info).mapToInt(StackInfo::getSize).sum();
user_1847300
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