我有一个堆栈的 ArrayList,在其中我将一个元素添加到其中一个堆栈并遍历列表,打印每个堆栈的索引。
然后我从前一个 Stack 中删除元素,将其添加到下一个 Stack,打印每个 Stack 的索引,然后对 ArrayList 中的所有 Stack 继续此操作。
但是,当任何堆栈为空时,在获取 ArrayList 中每个堆栈的索引时会出现非常不寻常的行为。不为空的 Stack将具有正确的索引值,而为空的Stack将具有不正确的索引值。
此外,似乎如果包含元素的堆栈位于索引 0 处,所有其他索引值都将为 1。如果包含元素的堆栈位于任何其他索引处,它将具有正确的索引值和所有其他索引值索引值将为 0。
这是我的代码:
import java.util.List;
import java.util.Stack;
import java.util.ArrayList;
public class ListOfStacks {
// instance variables:
List<Stack<Integer>> stacks;
private static final int NUMBER_OF_STACKS = 3;
// constructor:
ListOfStacks() {
this.stacks = new ArrayList<Stack<Integer>>(NUMBER_OF_STACKS);
// adding the stacks to the list here:
for (int i = 0; i < NUMBER_OF_STACKS; i++) {
this.stacks.add(new Stack<Integer>());
}
}
// instance methods:
void addElement(int stackIndex, int element) {
this.stacks.get(stackIndex).add(element);
}
void removeElement(int stackIndex) {
this.stacks.get(stackIndex).pop();
}
void printIndexes(int stackIndex, int element) {
System.out.printf("The stack at index %d now contains %d" +
"(the other stacks are empty):%n", stackIndex, element);
for (Stack<Integer> stack : this.stacks) {
System.out.printf("index %d%n", this.stacks.indexOf(stack));
}
System.out.println();
}
// main method:
public static void main(String[] args) {
ListOfStacks list = new ListOfStacks();
int index = 0, number = 5;
// adding the number 5 to the stack at index 0:
list.addElement(index, number);
list.printIndexes(index, number);
// now removing that element, and adding it to the stack at index 1:
list.removeElement(index++);
list.addElement(index, number);
list.printIndexes(index, number);
// now removing that element, and adding it to the stack at index 2:
list.removeElement(index++);
list.addElement(index, number);
list.printIndexes(index, number);
}
} // end of ListOfStacks
...这是输出(对于三个堆栈的 ArrayList):
The stack at index 0 now contains 5 (the other stacks are empty):
index 0
index 1
index 1
The stack at index 1 now contains 5 (the other stacks are empty):
index 0
index 1
index 0
The stack at index 2 now contains 5 (the other stacks are empty):
index 0
index 0
index 2