java - 根据指定顺序添加列表的更有效方法

Question

我有三个不同的 ArrayList 需要合并为一个，但是，它们在堆栈中的顺序很重要并且是指定的。我怎样才能更有效地做到这一点？

代码所做的是将 ArrayList 添加到完整 ArrayList 的适当级别(0,1,2)，但是有太多重复代码，因此该方法看起来很糟糕。

最终目标如下——我们关心的列与所需的顺序一起传递给我们的函数。然后，根据顺序，我们将其放在适当的位置，其他两列填充其余部分(它们的顺序无关)。

所以基本上，Column3 被传递，例如，顺序为 2。这意味着我们希望完整的 ArrayList 是 Column1 的内容，然后是 Column3 的内容，然后是 Column2 的内容(其中 Column1 和 Column2 可以交换，因为它们的顺序实际上并不相同)事)。

谢谢。

public void assemble(List<Card> selection, int order) {

        switch(order) {
            case 0:
                trickDeck.addAll(selection.stream().collect(Collectors.toList()));
                if (selection == column1) {
                    trickDeck.addAll(column2.stream().collect(Collectors.toList()));
                    trickDeck.addAll(column3.stream().collect(Collectors.toList()));
                }
                else if (selection == column2) {
                    trickDeck.addAll(column1.stream().collect(Collectors.toList()));
                    trickDeck.addAll(column3.stream().collect(Collectors.toList()));
                }
                else {
                    trickDeck.addAll(column1.stream().collect(Collectors.toList()));
                    trickDeck.addAll(column2.stream().collect(Collectors.toList()));
                }
                break;
            case 1:
                if (selection == column1) {
                    trickDeck.addAll(column2.stream().collect(Collectors.toList()));
                    trickDeck.addAll(selection.stream().collect(Collectors.toList()));
                    trickDeck.addAll(column3.stream().collect(Collectors.toList()));
                }
                else if (selection == column2) {
                    trickDeck.addAll(column1.stream().collect(Collectors.toList()));
                    trickDeck.addAll(selection.stream().collect(Collectors.toList()));
                    trickDeck.addAll(column3.stream().collect(Collectors.toList()));
                }
                else {
                    trickDeck.addAll(column1.stream().collect(Collectors.toList()));
                    trickDeck.addAll(selection.stream().collect(Collectors.toList()));
                    trickDeck.addAll(column2.stream().collect(Collectors.toList()));
                }
                break;
            case 2:
                if (selection == column1) {
                    trickDeck.addAll(column2.stream().collect(Collectors.toList()));
                    trickDeck.addAll(column3.stream().collect(Collectors.toList()));
                    trickDeck.addAll(selection.stream().collect(Collectors.toList()));
                }
                else if (selection == column2) {
                    trickDeck.addAll(column1.stream().collect(Collectors.toList()));
                    trickDeck.addAll(column3.stream().collect(Collectors.toList()));
                    trickDeck.addAll(selection.stream().collect(Collectors.toList()));
                }
                else {
                    trickDeck.addAll(column1.stream().collect(Collectors.toList()));
                    trickDeck.addAll(column2.stream().collect(Collectors.toList()));
                    trickDeck.addAll(selection.stream().collect(Collectors.toList()));
                }
                break;
            default:
                break;
        }
    }

Answer 1

我建议使用列索引而不是传入实际的List。然后我们可以将列作为数组进行操作。这是未经测试的演示:

public void assemble(int selection, int position) {
    // create list of columns
    List<List<Card>> columns = Arrays.asList(column1, column2, column3);

    // if selected column is not located at position, swap:
    if (selection != position) {
        List<Card> temp = columns.get(position);
        columns.set(position, columns.get(selection));
        columns.set(selection, temp);
    }

    // add all columns to trickDeck in order
    columns.forEach(trickDeck::addAll);
}