我正在嘗試實作一個調整大小函式，該函式根據 Scala3 中的元素數量和陣列大小來縮小和擴大陣列堆疊。這是我的代碼如下：
package adt
import scala.reflect.ClassTag
class ArrayStack[A: ClassTag]:
private var dataArray: Array[A] = Array.fill(10)(null.asInstanceOf[A])
private var top: Int = 0
private var sz: Int = 10
def push(elem: A): Unit =
if top == sz then resize(grow = true)
dataArray(top) = elem
top = 1
def pop(): A =
if top == (sz / 2) - 1 then resize(grow = false)
top -= 1
dataArray(top)
def peek(): A =
dataArray(top - 1)
def isEmpty(): Boolean =
top == 0
def resize(grow: Boolean): Unit =
val newSize = if grow then sz * 2 else sz / 2
val newArray: Array[A] = Array.fill(newSize)(null.asInstanceOf[A])
for (a <- 0 until dataArray.length) do newArray(a) = dataArray(a)
dataArray = newArray
sz = newSize
但是，在我的 JUnit 測驗中，我得到一個陣列索引越界例外。
@Test def pushMultiple(): Unit =
val stack = new ArrayStack[Int]
val pushArr = Array.tabulate(100)(i => Math.round(i * 100))
pushArr.foreach(stack.push(_))
for (n <- pushArr.reverse) do assertEquals(n, stack.pop())
@Test def popMultiple(): Unit =
val stack = new ArrayStack[Int]
val pushArr = Array.tabulate(100)(i => Math.round(i * 100))
pushArr.foreach(stack.push(_))
for (i <- 1 to 1000) do stack.pop()
assertTrue(stack.isEmpty())
錯誤資訊：
Test arraystack_test.pushMultiple failed: java.lang.ArrayIndexOutOfBoundsException: Index 80 out of bounds for length 80, took 0.032 sec
at scala.runtime.ScalaRunTime$.array_update(ScalaRunTime.scala:75)
ScalaRunTime.scala:75
at adt.ArrayStack.resize$$anonfun$1(ArrayStack.scala:30)
ArrayStack.scala:30
at scala.runtime.java8.JFunction1$mcVI$sp.apply(JFunction1$mcVI$sp.scala:18)
at scala.collection.immutable.Range.foreach(Range.scala:190)
Range.scala:190
at adt.ArrayStack.resize(ArrayStack.scala:30)
ArrayStack.scala:30
at adt.ArrayStack.pop(ArrayStack.scala:17)
ArrayStack.scala:17
at arraystack_test.pushMultiple$$anonfun$2(arraystack_test.scala:26)
at scala.runtime.java8.JFunction1$mcVI$sp.apply(JFunction1$mcVI$sp.scala:18)
at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1324)
ArrayOps.scala:1324
at arraystack_test.pushMultiple(arraystack_test.scala:26)
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
NativeMethodAccessorImpl.java:34
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
NativeMethodAccessorImpl.java:62
at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
DelegatingMethodAccessorImpl.java:43
at java.lang.reflect.Method.invoke(Method.java:566)
Method.java:566
...
Test arraystack_test.popMultiple failed: java.lang.ArrayIndexOutOfBoundsException: Index 80 out of bounds for length 80, took 0.0 sec
at scala.runtime.ScalaRunTime$.array_update(ScalaRunTime.scala:75)
ScalaRunTime.scala:75
at adt.ArrayStack.resize$$anonfun$1(ArrayStack.scala:30)
ArrayStack.scala:30
at scala.runtime.java8.JFunction1$mcVI$sp.apply(JFunction1$mcVI$sp.scala:18)
at scala.collection.immutable.Range.foreach(Range.scala:190)
Range.scala:190
at adt.ArrayStack.resize(ArrayStack.scala:30)
ArrayStack.scala:30
at adt.ArrayStack.pop(ArrayStack.scala:17)
ArrayStack.scala:17
at arraystack_test.popMultiple$$anonfun$2(arraystack_test.scala:32)
at scala.runtime.java8.JFunction1$mcII$sp.apply(JFunction1$mcII$sp.scala:17)
at scala.collection.immutable.Range.foreach(Range.scala:190)
Range.scala:190
at arraystack_test.popMultiple(arraystack_test.scala:32)
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
NativeMethodAccessorImpl.java:34
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
NativeMethodAccessorImpl.java:62
at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
DelegatingMethodAccessorImpl.java:43
at java.lang.reflect.Method.invoke(Method.java:566)
誰能幫我弄清楚為什么我的調整大小縮小功能不起作用？
uj5u.com熱心網友回復：
沒關系，我想通了。
在resize方法中，這會導致索引越界例外
for (a <- 0 until dataArray.length) do newArray(a) = dataArray(a)
當該方法被呼叫時，它作業正常。但是，當呼叫該方法進行shrink 時，newArray 的長度是dataArray 的一半，因此會導致索引越界例外。
要解決此問題：
def resize(grow: Boolean): Unit =
val newSize = if grow then sz * 2 else sz / 2
val endRange: Int = if grow then dataArray.length else newSize
val newArray: Array[A] = Array.fill(newSize)(null.asInstanceOf[A])
for (a <- 0 until endRange) do newArray(a) = dataArray(a)
dataArray = newArray
sz = newSize
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