Remove Double Negative（去除雙重否定）

WHAT

雙重否定的條件語句，可以使用一個肯定的條件語句代替

記住：雙重否定 = 肯定

本次重構涉及到的基本重構手法：

1. Extract Method（提煉方法）
2. Inline Method（内聯方法）
3. Substitute Algorithm（替換算法）

WHEN

雙重否定，雖然機器能夠很好了解并正确執行，但是不符合人的自然語言習慣，且令人迷惑，降低代碼可讀性

HOW

重構前的代碼

package remove.doubles.negative;

public class SomeClass {
	
	private boolean found = false;

	public boolean isNotFound() {
		return !found;
	}

	public void someMethod() {
		if (!isNotFound()) { // double negative
			// do something
		}
	}
	
	public void someMethod2() {
		if (isNotFound()) { // negative
			// do something else
		}
	}
	
}
           

重構步驟

• 提煉肯定條件方法：選中否定條件方法中的肯定部分（如果現在沒有，替換算法，杜撰一個），使用快捷鍵（Alt + Shitf + M）或者上下文菜單（Refactor -> Extract Method ... ），彈出” Extract Method“對話框 

  

  

• 方法名取名為：isFound，并選擇Access Modifier為public，提取函數之後的代碼

package remove.doubles.negative;

public class SomeClass {
	
	private boolean found = false;

	public boolean isNotFound() {
		return !isFound();
	}

	public boolean isFound() {// extracted positive conditional method
		return found;
	}

	public void someMethod() {
		if (!isNotFound()) { // double negative
			// do something
		}
	}
	
	public void someMethod2() {
		if (isNotFound()) { // negative
			// do something else
		}
	}
	
}
           

• 針對每一個雙重否定條件，将雙重否定改為肯定
  • 先内聯否定條件方法：在調用處，選擇否定條件，使用快捷鍵（Alt + Shit + I）或者上下文菜單（Refactor -> Inline...），彈出“Inline Method”對話框，選擇“Only the selected invocation”

    

    

  • 重構後的代碼 

package remove.doubles.negative;

public class SomeClass {
	
	private boolean found = false;

	public boolean isNotFound() {
		return !isFound();
	}

	public boolean isFound() {// extracted positive conditional method
		return found;
	}

	public void someMethod() {
		if (!!isFound()) { // double negative, after inline method 
			// do something
		}
	}
	
	public void someMethod2() {
		if (isNotFound()) { // negative
			// do something else
		}
	}
	
} 
           

• • 替換算法，把雙重否定改為肯定

package remove.doubles.negative;

public class SomeClass {
	
	private boolean found = false;

	public boolean isNotFound() {
		return !isFound();
	}

	public boolean isFound() {// extracted positive conditional method
		return found;
	}

	public void someMethod() {
		if (isFound()) { // changed double negative to positive
			// do something
		}
	}
	
	public void someMethod2() {
		if (isNotFound()) { // negative
			// do something else
		}
	}
	
}
           

• 最後，如果否定條件方法isNotFound()，沒有調用，使用隐藏方法（Hidden Method），或者隻有少數幾個調用，使用内聯方法：Inline method 
  • 選中 isNotFound方法， 使用快捷鍵（Alt + Shit + I）或者上下文菜單（Refactor -> Inline...），彈出“Inline Method”對話框，選擇“All invocations”，并選擇“Delete method declaration”

    

    

重構後的代碼

package remove.doubles.negative;

public class SomeClass {
	
	private boolean found = false;

	public boolean isFound() {// extracted positive conditional method
		return found;
	}

	public void someMethod() {
		if (isFound()) { // changed double negative to positive
			// do something
		}
	}
	
	public void someMethod2() {
		if (!isFound()) { // changed negative to use not positive
			// do something else
		}
	}
	
}