Remove Double Negative（去除双重否定）
WHAT

双重否定的条件语句，可以使用一个肯定的条件语句代替

记住：双重否定 = 肯定

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本次重构涉及到的基本重构手法：

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Extract Method（提炼方法）Inline Method（内联方法）Substitute Algorithm（替换算法）

WHEN

双重否定，虽然机器能够很好理解并正确执行，但是不符合人的自然语言习惯，且令人迷惑，降低代码可读性

HOW重构前的代码

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}}}

重构步骤提炼肯定条件方法：选中否定条件方法中的肯定部分（如果现在没有，替换算法，杜撰一个），使用快捷键（Alt + Shitf + M）或者上下文菜单（Refactor -> Extract Method ...?），弹出”?Extract Method“对话框?

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?方法名取名为：isFound，并选择Access Modifier为public，提取函数之后的代码

package remove.doubles.negative;public class SomeClass {private boolean found = false;public boolean isNotFound() {return !isFound();}public boolean isFound() {// extracted positive conditional methodreturn found;}public void someMethod() {if (!isNotFound()) { // double negative// do something}}public void someMethod2() {if (isNotFound()) { // negative// do something else}}}

针对每一个双重否定条件，将双重否定改为肯定先内联否定条件方法：在调用处，选择否定条件，使用快捷键（Alt + Shit + I）或者上下文菜单（Refactor -> Inline...），弹出“Inline Method”对话框，选择“Only the selected invocation”

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?重构后的代码?

package remove.doubles.negative;public class SomeClass {private boolean found = false;public boolean isNotFound() {return !isFound();}public boolean isFound() {// extracted positive conditional methodreturn found;}public void someMethod() {if (!!isFound()) { // double negative, after inline method // do something}}public void someMethod2() {if (isNotFound()) { // negative// do something else}}}?

替换算法，把双重否定改为肯定

package remove.doubles.negative;public class SomeClass {private boolean found = false;public boolean isNotFound() {return !isFound();}public boolean isFound() {// extracted positive conditional methodreturn found;}public void someMethod() {if (isFound()) { // changed double negative to positive// do something}}public void someMethod2() {if (isNotFound()) { // negative// do something else}}}

最后，如果否定条件方法isNotFound()，没有调用，使用隐藏方法（Hidden Method），或者只有少数几个调用，使用内联方法：Inline method?选中isNotFound方法，使用快捷键（Alt + Shit + I）或者上下文菜单（Refactor -> Inline...），弹出“Inline Method”对话框，选择“All invocations”，并选择“Delete method declaration”

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?重构后的代码

package remove.doubles.negative;public class SomeClass {private boolean found = false;public boolean isFound() {// extracted positive conditional methodreturn 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}}}

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