arrays - 常规数组。 [[],[]].toArray() 和 [[],[]]*.toArray() 之间有什么区别

Question

我已经在groovy中准备了用于参数化单元测试的数据:

@Parameterized.Parameters
static List data() {
    [
            ['20101113', 'DATE',
             '20101114', 'DATE',
             'some statement',
             '20101101T000000/20110101T000000',
             null,
             ['some', 'expected', 'data', 'results']]
    // ...and other 
    ]*.toArray()
}

它工作正常。我检查了此代码，并尝试简化将 ]*.toArray() 替换为 ].toArray()。

java.lang.Exception: FirstParametrizedTest.data() must return a Collection of arrays.

at org.junit.runners.Parameterized$TestClassRunnerForParameters.computeParams(Parameterized.java:94)
at org.junit.runners.Parameterized$TestClassRunnerForParameters.createTest(Parameterized.java:86)
at org.junit.runners.BlockJUnit4ClassRunner$1.runReflectiveCall(BlockJUnit4ClassRunner.java:236)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
at org.junit.runners.BlockJUnit4ClassRunner.methodBlock(BlockJUnit4ClassRunner.java:233)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:68)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:47)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:231)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:60)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:229)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:50)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:222)
at org.junit.runners.ParentRunner.run(ParentRunner.java:300)
at org.junit.runners.Suite.runChild(Suite.java:128)
at org.junit.runners.Suite.runChild(Suite.java:24)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:231)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:60)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:229)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:50)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:222)
at org.junit.runners.ParentRunner.run(ParentRunner.java:300)
at org.junit.runner.JUnitCore.run(JUnitCore.java:157)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:51)
at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:237)
at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)

我恢复了我的更改并且它有效，但我不明白为什么指令 ].toArray() 是意外的？ ].toArray() 是如何工作的以及 ].toArray() 和 ]*.toArray() 之间有什么区别？

Answer 1

来自doc , *. 称为扩展运算符并返回一个列表。

The Spread Operator (*.) is used to invoke an action on all items of an aggregate object. It is equivalent to calling the action on each item and collecting the result into a list:

如果没有*，toArray只是返回一个对象数组，当然数组不能在运行时转换为List。

---

使用*，您当前的代码会执行以下操作:

  static List data() {
        def result = []
        List input = [
                ['20101113', 'DATE',
                 '20101114', 'DATE',
                 'some statement',
                 '20101101T000000/20110101T000000',
                 null,
                 ['some', 'expected', 'data', 'results']]
                // ...and other
        ]

        for (def item : input) {
            result.add(item != null ? ((List) item).toArray() : null)
        }

        result
    }