英文:
How to convert List<FirstObject[]> to List<SecondObject> with Stream in Java 8?
问题
我有列表：
List<Point[]> listPoints = ...
List<Quadrangle> quadrangles = ...
如何使用 Java 8 中的 Stream 将 List<Point[]> 转换为 List<Quadrangle>？
需要替换：
for(Point[] groupPoints : listPoints) {
quadrangles.add(new Quadrangle(groupPoints));
}
Quadrangle 对象具有构造函数：
public Quadrangle(Point[] points) {
this.p1 = points[0];
this.p2 = points[1];
this.p3 = points[2];
this.p4 = points[3];
}
我尝试了这个：
List<Quadrangle> quadrangles = listPoints.stream()
.map(groupPoints -> new Quadrangle(groupPoints))
.collect(Collectors.toList());
但是这对我不起作用。我得到了错误：
需要的类型：Point[]
提供的类型：<lambda parameter>
我认为 lambda parameter o 是数组 Point[]，但实际上并不是这样。
英文:
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.
答案1
得分: 2
尝试这样做：
- 将点数组列表进行流式处理。
- 映射到四边形的新实例（这将应用构造函数参数）。
- 返回四边形的列表。
List<Quadrangle> quads = listPoints.stream()
.map(Quadrangle::new)
.collect(Collectors.toList());
英文:
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());
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