Java:从另一个数组的属性创建一个数组 [英] Java: Creating an Array from the Properties of Another Array

问题描述

Java中是否有一种简单的方法(不涉及编写for循环)来从另一个不同对象数组的属性创建对象数组?

Is there a simple way in Java (that doesn't involve writing a for-loop) to create an array of objects from a property of another array of different objects?

例如，如果我有一个类型为 A 的对象数组，则定义为:

For example, if I have an array of objects of type A, defined as:

public class A {
    private String p;
    public getP() {
        return p;
    }
}

我想创建一个字符串数组，其中包含每个 i 的 A [i] .p 值.

I want to create an array of Strings that contains the value of A[i].p for each i.

基本上，我要这样做:

Essentially, I'm I want to do this: Creating an array from properties of objects in another array, but in Java.

我试图将 Arrays.copyOf(U [] original，int newLength，Class<?extended T []> newType)连同lambda表达式一起使用，但这似乎并没有工作.我尝试过的:

I attempted to use Arrays.copyOf(U[] original, int newLength, Class<? extends T[]> newType) along with a lambda expression, but that didn't seem to work. What I tried:

Arrays.copyOf(arrayA, arrayA.length, (A a) -> a.getP());

推荐答案

在Java 8中，您可以使用 Stream API，尤其是 map 函数:

With Java 8, you can use the Stream API and particularly the map function:

A[] as = { new A("foo"), new A("bar"), new A("blub") };
String[] ps = Stream.of(as).map(A::getP).toArray(String[]::new);

在这里， A :: getP 和 String [] :: new 是方法/构造函数引用.如果您没有想要的属性的合适方法，则还可以使用lambda函数:

Here, A::getP and String[]::new are method/constructor references. If you do not have a suitable method for the property you want to have, you could also use a lambda function:

String[] ps = Stream.of(as).map(a -> a.getP()).toArray(String[]::new);

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