java - Android 性能 - 'Avoid Internal Getters/Setters'

Question

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Avoid Internal Getters/Setters

In native languages like C++ it's common practice to use getters (e.g. i = getCount()) instead of accessing the field directly (i = mCount). This is an excellent habit for C++, because the compiler can usually inline the access, and if you need to restrict or debug field access you can add the code at any time.

On Android, this is a bad idea. Virtual method calls are expensive, much more so than instance field lookups. It's reasonable to follow common object-oriented programming practices and have getters and setters in the public interface, but within a class you should always access fields directly.

Without a JIT, direct field access is about 3x faster than invoking a trivial getter. With the JIT (where direct field access is as cheap as accessing a local), direct field access is about 7x faster than invoking a trivial getter. This is true in Froyo, but will improve in the future when the JIT inlines getter methods.

2019/05 更新:在当前版本中，上述 Material 已从文档中删除!

也就是说你会在类中使用字段访问:

 public class MyObject {

    public Object innerObject; // This would be private if I was using a getter

    public void doSomeStuff(){
          if(innerObject){        // Within class access like this
                 // ....
          }
    }

    public Object getInnerObject(){  // This would be removed if I was using field access
         return innerObject;
    }
 }

但是从另一个对象访问呢？:

 public class SecondObject {

      public void doSecondSomething(){
                MyObject ob = new MyObject();
                Object inner;

                //This is my question basically (from an Android performance perspective)   
                inner = ob.getInnerObject();
                // OR 
                inner = b.innerObject

       }

 }

Answer 1

使用内部 getter 和 setter 对性能的影响也适用于外部 getter 和 setter。

但是，在外部情况下，getter 和 setter 在其他领域具有显着优势；例如保留封装、减少有害耦合、使您的代码更易于维护等等。因此，尽管可能会导致性能下降，但使用 getter 和 setter 通常被认为是最佳实践。

性能下降是由于旧版 Android JIT 编译器的限制所致。这种情况在使用 Gingerbread 后得到了显着改善(请参阅 - https://stackoverflow.com/a/4930538/139985 ...并注意谁写了这个答案!)并继续改善。事实上，在当前 (2019) 版本的 Performance Tips 中，有关内部 getter 和 setter 的整个部分已被删除。

一般来说，为劣质平台“调整”代码是个坏主意，尤其是在有可能出现更好的平台时。