java - 按需创建 Java 对象

Question

我有一个java私有(private)方法，我试图找到在该方法内创建对象的最佳方法。以下是我正在尝试的两种不同方法:

方法A:

 private void createObject() {
     Object A;
     if (conditionA) {
         A = new Object();
         //do some Action X with object A
     } else {
         //Do something without object A
         if (conditionB) {
             return;
         }
         A = new Object();
         //do some Action Y with object A
     }
     return;
 }

方法B:

 private void createObject() {
     Object A = new Object()
     if (conditionA) {
         //do some action X with Object A
     } else {
         //Do something without Object A
         if (conditionB) {
             return;
         }
         //do some action Y with Object A
     }
     return;
 }

显然这两个代码片段都可以工作并且没有任何问题。我只是想找出更好的编码风格和标准。

Answer 1

让我们写出真值表

  A  |   B   |      Expected Outcome               
-----+-------+-------------------------------
True | True  | do X with object A               
True | False | do X with object A               
False| False | do Y with object A               
False| True  | do something without object A 
-----+-------+-------------------------------

我认为这可以翻译为:

boolean doXWithA = conditionA;
boolean doYWithA = !conditionA && !conditionB;
boolean doSomethingWithA = doXWithA || doYWithA;
if(doSomethingWithA)
    Object a = new Object();
    if (doXWithA) {
        // do X with object A 
    } else if (doXWithB) {
        // do X with object B 
    }
} else {
    // do something without object A 
}

好的做法是尽可能缩小变量的范围。如果实例化的成本很高，您还希望减少实例化的次数。这里对象a仅在必要时初始化，并且其范围尽可能小(只有一个if block )