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Decompose Conditional : 將Expression表達式結果明確命名為Method

if (星期一 < Parameter && Parameter < 星期三)  => if ( IsTuesday()) 好處 : 不用在看條件在寫什麼，很直覺的看方法名稱，就知在處理什麼事

Consolidate Conditional Expression : 多if 的 Expression 且回傳相同，將多if 的 Expression 下的Conditional 提取一個Method，回傳值

if (Parameter < 10) return 1
else if (parameter < 20 ) return 1
else if (parameter > 40) return 1  => if (Isthirty()) return 1;

Consolidate Duplicate Conditional Fragments : 多if 的 Expression，有相同method，未return，則將Method放至最後

if (Parameter < 10) {
  a = 1; 
  finishParameter(); 
} else {
  b = 1; 
  finishParameter(); 
}
=>
if (Parameter < 10) 
  a = 1; 
else 
  b = 1; 
  
finishParameter(); 

Remove Control Flag : 於迴圈內，無外部標記影響，則使用break、continue、，若Method 則可用 return

function Test() {
  bool IsStop = false;
  for (int i =0; i < 10 ; i++) {
    if (! IsStop && i > 5)
        IsStop = true;
  }} =>

function Test() {
 for (int i =0; i < 10 ; i++) {
    if (! IsStop && i > 5) break;
 }}

Replace Nested Conditional with Guard Clauses : 多層的If，若某層的if，條件表達式與上下層無影響，則可拉至同一層

string Week = '';
if ( isMonDay)
  Week = MonDay
else {
  if (isTuesDay()) {
      Week = TuesDay;
  else
      Week = OtherDay;
}}  =>

if ( isMonDay())
  Week = MonDay
else if (isTuesDay())
  Week = TuesDay;
else
  Week = OtherDay;

Replace Conditional with Polymorphism : 與oop有關，if 、switch 的條件運算式，依某類別延伸，而執行某類別方法，則可使用Strategy Pattern、Simple Factory

Week week = new Week('星期二');
IDay day = new Day(week); //Simple Factory 
day.getWeek();
}}

Day(Week){
if (week.name === '星期一')
 return new Monday(); //Strategy Pattern Interface方法就不寫了，請去看Strategy Pattern
else if (week.name === '星期二')
 return new Tuesday(); //Strategy Pattern
else if (week.name === '星期三'
 return new Wednesday(); //Strategy Pattern
}

Introduce Null Object 當條件表達式有null時，則多null物件來回傳型別初始值

Day(Week){
if (week.name === '星期一')
 return new Monday(); //Strategy Pattern Interface方法就不寫了，請去看Strategy Pattern
else if (week.name === '星期二')
 return new Tuesday(); //Strategy Pattern
else if (week.name === undefind)
 return new UndefindObject(); //Strategy Pattern
}

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盡量轉為 c#、Js

ref : https://www.tenlong.com.tw/products/9787115369093