重複代碼的命令類的Java

Question

我有一個實現命令（使用命令模式）這兩個類，一類是創建片：

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); 
    } 
} 

，另一個是刪除：

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); 
    } 
} 

我怎樣才能避免這個重複的代碼？

謝謝！

Answer 1

您可以創建一個兩個命令都可以實現的中間抽象類。

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(); 
} 

然後你的子類會小得多：

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); } 
} 

關於這樣做的好處是，你可以很容易地添加在相同的「類別」的新命令（這麼說）具有更多具體功能。

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

對於您這樣的短代碼，您通過嘗試消除代碼來節省很少的代碼，並且保存的代碼越多，解決方案就越複雜。

但是，這裏有一個可能的Java 8實現使用抽象類。

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)); 
    } 
} 

該實現使用lambda表達式來表達您需要執行的操作。因爲lambda表達式是閉包，所以不需要明確保留實際的工作簿和表名引用 - 它們隱藏在lambda表達式中。

對於execute和undo中更復雜的代碼，您可能會更好地按照原來的方式編寫這些方法，如果您嘗試使用lambda表達式，那麼最終的代碼將更復雜且難以讀取你原來有。