重复代码命令 Class Java

Question

我有两个类实现命令（使用命令模式），一个是创建 sheet:

public class CommandCreateSheet implements Command {

    private Workbook workbook;
    private String sheetName;

    public CommandCreateSheet(Workbook workbook, String workSheetName) {
        this.workbook = workbook;
        this.sheetName = workSheetName;
    }

    @Override
    public void execute() {
        this.workbook.addSheet(this.sheetName);
    }

    @Override
    public void undo() {
        this.workbook.removeSheet(this.sheetName);
    }
}

另一个是删除：

public class CommandDeleteSheet implements Command {

    private Workbook workbook;
    private String sheetName;

    public CommandDeleteSheet(Workbook workbook, String workSheetName) {
        this.workbook = workbook;
        this.sheetName = workSheetName;
    }

    @Override
    public void execute() {
        this.workbook.removeSheet(this.sheetName);
    }

    @Override
    public void undo() {
        this.workbook.addSheet(this.sheetName);
    }
}

如何避免重复代码？

谢谢！！

Answer 1

您可以创建两个命令都实现的中间摘要 class。

public abstract class AbstactSheetCommand implements Command
{
    private Workbook workbook;
    private String sheetName;

    protected AbstractSheetCommand(Workbook workbook, String workSheetName)
    {
        this.workbook = workbook;
        this.sheetName = workSheetName;
    }

    public abstract void execute();
    public abstract void undo();
}

然后你的子class会小很多：

public class CommandCreateSheet extends AbstractSheetCommand
{
    public CommandCreateSheet(Workbook workbook, String workSheetName)
    {
        super(workbook, workSheetName);
    }

    @Override
    public void execute() { this.workbook.addSheet(this.sheetName); }

    @Override
    public void undo() { this.workbook.removeSheet(this.sheetName);}
}

public class CommandDeleteSheet extends AbstractSheetCommand
{
    public CommandDeleteSheet(Workbook workbook, String workSheetName)
    {
        super(workbook, workSheetName);
    }

    @Override
    public void execute() { this.workbook.removeSheet(this.sheetName); }

    @Override
    public void undo() { this.workbook.addSheet(this.sheetName); }
}

这样做的好处是，您可以轻松地添加具有更具体功能的相同 "category"（可以这么说）的新命令。

public class CommandRenameSheet extends AbstractSheetCommand
{
    private String newWorkSheetName;

    public CommandDeleteSheet(Workbook workbook, String oldWorkSheetName, String newWorkSheetName)
    {
        super(workbook, oldWorkSheetName);
        this.newWorkSheetName = newWorkSheetName;
    }

    @Override
    public void execute() 
    { this.workbook.renameSheet(this.sheetName, newWorkSheetName); }

    @Override
    public void undo() 
    { this.workbook.renameSheet(newWorkSheet, this.sheetName); }
}

Answer 2

对于像你这样短的代码，你通过尝试消除代码来节省很少，而且你节省的代码越多，你的解决方案就越复杂。

但是这里有一个可能的 Java 8 实现使用抽象 class。

public abstract class SheetCommand implements Command {

    private Runnable executeAction, undoAction;

    public SheetCommand(Runnable executeAction, Runnable undoAction) {
        this.executeAction = executeAction;
        this.undoAction = undoAction;
    }

    @Override
    public void execute() {
        executeAction.run();
    }

    @Override
    public void undo() {
        undoAction.run();
    }
}

public class CommandCreateSheet extends SheetCommand {

    public CommandCreateSheet(Workbook workbook, String workSheetName) {
        super(() -> workbook.addSheet(workSheetName),
              () -> workbook.removeSheet(workSheetName));
    }
}

public class CommandDeleteSheet extends SheetCommand {

    public CommandDeleteSheet(Workbook workbook, String workSheetName) {
        super(() -> workbook.removeSheet(workSheetName),
              () -> workbook.addSheet(workSheetName));
    }
}

此实现使用 lambda 表达式来表达您需要执行的操作。因为 lambda 表达式是闭包，所以您不需要显式保留实际的工作簿和 sheet 名称引用 - 它们隐藏在 lambda 表达式中。

对于 execute 和 undo 中更复杂的代码，您可能会像最初那样自己编写方法来做得更好 - 如果您尝试使用 lambda 来完成，您将结束编写比您最初拥有的代码更复杂、更难读的代码。

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