How to convert List<FirstObject[]> to List<SecondObject> with Stream in Java 8? [duplicate]

Question

I have lists:

List<Point[]> listPoints = ...
List<Quadrangle> quadrangles = ...

How convert List<Point[]> to List<Quadrangle> with Stream in Java 8?

Need replace:

for(Point[] groupPoints : listPoints) {
            quadrangles.add(new Quadrangle(groupPoints));
}

Object Quadrangle has the constructor:

public Quadrangle(Point[] points) {
        this.p1 = points[0];
        this.p2 = points[1];
        this.p3 = points[2];
        this.p4 = points[3];
    }

I tried this:

List<Quadrangle> quadrangles = listPoints.stream()
                .collect(Collectors.toCollection(o -> new Quadrangle(o)));

but this doesn't work for me. I get error:

Required  type:Point[]
Provided: <lambda parameter>

I thought that the lambda parameter o is the array Point [], but isn't it.

WJS · Accepted Answer · 2020-08-31 00:09:09Z

2

Try it like this.

Stream the list of point arrays.
Map to a new instance of Quadrangle (this applies the constructor argument)
return a list of Quadrangle.

List<Quadrangle> quads = listPoints.stream()
.map(Quadrangle::new)
.collect(Collectors.toList());

edited Aug 31, 2020 at 0:09

answered Aug 30, 2020 at 23:58

WJS

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