重复代码的命令类的Java

Question

我有一个实现命令（使用命令模式）这两个类，一类是创建片：

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); 
    } 
} 

我怎样才能避免这个重复的代码？

谢谢！

Answer 1

您可以创建一个两个命令都可以实现的中间抽象类。

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(); 
} 

然后你的子类会小得多：

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); } 
} 

关于这样做的好处是，你可以很容易地添加在相同的“类别”的新命令（这么说）具有更多具体功能。

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

对于您这样的短代码，您通过尝试消除代码来节省很少的代码，并且保存的代码越多，解决方案就越复杂。

但是，这里有一个可能的Java 8实现使用抽象类。

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)); 
    } 
} 

该实现使用lambda表达式来表达您需要执行的操作。因为lambda表达式是闭包，所以不需要明确保留实际的工作簿和表名引用 - 它们隐藏在lambda表达式中。

对于execute和undo中更复杂的代码，您可能会更好地按照原来的方式编写这些方法，如果您尝试使用lambda表达式，那么最终的代码将更复杂且难以读取你原来有。