演员表＆LT;对象[]＆GT;到对象[] []在Java中 [英] Cast List<Object[]> to Object[][] in Java

问题描述

如何打开列表阵列成二维数组在Java中？

  // prepare名单
清单＆LT;对象[]＆GT; CONF =新的LinkedList＆LT;对象[]＆GT;（）;
conf.add（新的对象[] {FOO，BAR}）;
conf.add（新的对象[] {FOO，BAR}）;
 

我试过：

 对象[] []数组=（对象[] []）conf.toArray（新对象[0]​​）;
 

但它在 ClassCastException异常失败：

 了java.lang.RuntimeException：java.lang.ClassCastException：[Ljava.lang.Object;不能转换为[Ljava.lang.Object;
 

解决方案

您缺少一对括号的：

 对象[] []数组= conf.toArray（新对象[0]​​ []）;
                                                 ^^
 

或者，如果你想保存在一个不必要的内存分配：

 对象[] []数组= conf.toArray（新对象[conf.size（）] []）;
 

演员到对象[] [] 是不必要的，一旦参数的toArray（）具有正确的类型

How to turn List of arrays into two dimensional array in Java?

//Prepare the list
List<Object[]> conf = new LinkedList<Object[]>();
conf.add(new Object[]{ "FOO", "BAR"});
conf.add(new Object[]{ "FOO", "BAR"});

I tried:

Object[][] array = (Object[][]) conf.toArray(new Object[0]);

But it fails at ClassCastException:

java.lang.RuntimeException: java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [[Ljava.lang.Object;

解决方案

You are missing a pair of square brackets:

    Object[][] array = conf.toArray(new Object[0][]);
                                                 ^^

Or, if you wish to save on one unnecessary memory allocation:

    Object[][] array = conf.toArray(new Object[conf.size()][]);

The cast to Object[][] is unnecessary once the argument to toArray() has the correct type.

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