巢狀條件式通常為為複雜度高的區域。
以下紀錄簡化巢狀條件式的技巧
1.巢狀 if 轉換成 if then else + and。
先從最簡單的開始，e.g.
private String nestedCondition1()
{
String result = "";
if (isProcess) {
if (isDone) {
return result = result.concat("process is truedone is true");
}
}
return result;
}
目標是第4和第5行巢狀if，我們使用 if + and，化解巢狀if。
private String fixByIfThenElse1()
{
String result = "";
if (isProcess && isDone) {
return result = result.concat("process is truedone is true");
}
return result;
}
2.變化：原式 if 和 if 之間有statement。e.g.第5行新增 result = result.concat(“process is true”);
private String nestedCondition2()
{
String result = "";
if (isProcess) {
result = result.concat("process is true");
if (isDone) {
return result = result.concat("done is true");
}
}
return result;
}
對於第5行有個轉換的小技巧。在2個 if 之間的 statement 可以轉換為 if(condition1 && ! condition2){statement};
需要注意的是 condition2 必須反轉。e.g.
if(condition1){
statement1;
if(condition2){
statement2;
}
}
---------trans-----------
if(condition1 && !condition2){
statement1;
}else if(condition1 && condition2){
statement1;
statement2;
}
轉換 if-then-else + and
private String fixByIfThenElse2()
{
String result = "";
if(isProcess && !isDone){
result = result.concat("process is true");
}else if(isProcess && isDone){
result = result.concat("process is true");
result = result.concat("done is true");
}
return result;
}
3.變化： 原式最外層 if 產生相對應的 else。新增 9～11行
private String nestedCondition3()
{
String result = "";
if (isProcess) {
result = result.concat("process is true");
if (isDone) {
return result = result.concat("done is true");
}
} else {
result = result.concat("process is not true");
}
return result;
}
轉換 if-then-else + and，新增8～10行
private String fixByIfThenElse3()
{
String result = "";
if(isProcess && !isDone){
result = result.concat("process is true");
}else if(isProcess && isDone){
result = result.concat("process is true");
result = result.concat("done is true");
}else if(!isProcess){
result = result.concat("process is not true");
}
return result;
}
4.變化： 原式內層 if 產生相對應 else 。新增 8～10行
private String nestedCondition4()
{
String result = "";
if (isProcess) {
result = result.concat("process is true");
if (isDone) {
return result = result.concat("done is true");
} else {
return result = result.concat("done is not true");
}
} else {
result = result.concat("process is not true");
}
return result;
}
轉換 if-then-else + and
private String fixAndNestedConditionSimple()
{
String result = "";
if (isProcess && isDone) {
result = result.concat("process is true");
return result = result.concat("done is true");
} else if (isProcess && !isDone) {
result = result.concat("process is true");
return result = result.concat("done is not true");
} else if (!isProcess) {
result = result.concat("process is not true");
}
return result;
}
5.變化：外層 if 的 else 加入其他動作，12~17行
private String nestedCondition5()
{
String result = "";
if (isProcess) {
result = result.concat("process is true");
if (isDone) {
result = result.concat("done is true");
} else {
result = result.concat("done is not true");
}
} else {
result = result.concat("process is not true");
if (isPrint) {
result = result.concat("print is true");
} else {
result = result.concat("print is not true");
}
}
return result;
}
轉換對應的 if-then-else + and 為
private String fixByNestedCondition5()
{
String result = "";
if (isProcess && isDone) {
return result = result.concat("process is truedone is true");
} else if (isProcess && !isDone) {
return result = result.concat("process is truedone is not true");
} else if (!isProcess && isPrint) {
result = result.concat("process is not true");
return result = result.concat("print is true");
} else if (!isProcess && !isPrint) {
result = result.concat("process is not true");
return result = result.concat("print is not true");
}
return result;
}
總結：
照這種排列邏輯來看基本上所有的巢狀 if 都可以轉換 if then else + and的結構，差別只在於複雜度與可讀性的不同。
2.以衛述句取代巢狀條件式。
這個方法是從”重構：改善既有程式的設計”一書來的。
衛述句是指條件式中若有特別的判斷邏輯，必須明確的標示出來並立刻從函式中返回。e.g.
private String nestedCondition1()
{
String result = "";
if (isProcess) {
if (isDone) {
return result = result.concat("process is truedone is true");
}
}
return result;
}
以衛述句改善為
private String fixByGuardClause1()
{
String result = "";
if (!isProcess) {
return result;
}
if (isDone) {
return result = result.concat("process is truedone is true");
}
return result;
}
2.變化：原式 if 和 if 之間有statement。e.g.第5行新增 result = result.concat(“process is true”);
private String fixByGuardClauseOrigin()
{
String result = "";
if (isProcess) {
result = result.concat("process is true");
}else{
if (isDone) {
result = result.concat("done is true");
}else{
result = result.concat("done is not true");
}
}
return result;
}
以衛述句改善有2種形式，分別為是否在判斷邏輯加入 and 運算。
加入and運算後可以看到其第1種方式較為簡潔(不需要摻雜result = result.concat(“process is true”))，可讀性較高。
1.在判斷邏輯加入 and 。
private String fixByGuardClauseWithAnd2()
{
String result = "";
if(isProcess && !isDone){
return result = result.concat("process is true");
}
if(isProcess && isDone){
result = result.concat("process is true");
return result= result.concat("done is true");
}
return result;
}
2.不加入 and。
private String fixByGuardClause2()
{
String result = "";
if(!isProcess){
return result;
}
result = result.concat("process is true");
if(isDone){
return result = result.concat("done is true");
}
return result;
}
3.變化型： 原式最外層 if 產生相對應的 else。新增 9～11行
private String nestedCondition3()
{
String result = "";
if (isProcess) {
result = result.concat("process is true");
if (isDone) {
return result = result.concat("done is true");
}
} else {
result = result.concat("process is not true");
}
return result;
}
以衛述句改善為
private String fixByGuardClause3WithAnd()
{
String result = "";
if(!isProcess){
return result.concat("process is not true");
}
if(isProcess && !isDone){
return result.concat("process is true");
}
if(isProcess && isDone){
result = result.concat("process is true");
return result.concat("done is true");
}
return result;
}
4.變化： 原式內層 if 產生相對應 else 。新增 8～10行
private String nestedCondition4()
{
String result = "";
if (isProcess) {
result = result.concat("process is true");
if (isDone) {
return result = result.concat("done is true");
} else {
return result = result.concat("done is not true");
}
} else {
result = result.concat("process is not true");
}
return result;
}
以衛述句改善為
private String fixByGuardClause4WithAnd()
{
String result = "";
if(isProcess && !isDone){
result = result.concat("process is true");
return result = result.concat("done is not true");
}
if(isProcess && isDone){
result = result.concat("process is true");
return result = result.concat("done is true");
}
if(!isProcess){
return result = result.concat("process is not true");
}
return result;
}
5.變化：外層 if 的 else 加入其他動作，新增12~17行
private String nestedCondition5()
{
String result = "";
if (isProcess) {
result = result.concat("process is true");
if (isDone) {
result = result.concat("done is true");
} else {
result = result.concat("done is not true");
}
} else {
result = result.concat("process is not true");
if (isPrint) {
result = result.concat("print is true");
} else {
result = result.concat("print is not true");
}
}
return result;
}
以衛述句改善為
private String fixByGuardClause5WithAnd()
{
String result = "";
if (!isProcess && !isPrint) {
result = result.concat("process is not true");
result = result.concat("print is not true");
return result;
}
if (!isProcess && isPrint) {
result = result.concat("process is not true");
result = result.concat("print is true");
return result;
}
if (isProcess && isDone) {
result = result.concat("process is true");
result = result.concat("done is true");
return result;
}
if (isProcess && !isDone) {
result = result.concat("process is true");
result = result.concat("done is not true");
return result;
}
return result;
}
無論使用衛述句或是if-then-else都可將難以理解的巢狀結構分解成簡單的表達式。