哪个在性能，隐式（自动）拆箱或显式拆箱方面更好？ [英] Which is better in terms of performance, implicit (auto) unboxing or explicit unboxing?

问题描述

把它放在代码中 - 性能更好（如果有差异的话）？

To put it in code - which has better performance (if there is a difference at all)?

鉴于此：

public class Customer
{
    ....

    public Boolean isVIP(){...}
    ...
}

哪个更快？

public void handleCustomer(Customer customer)
{
    if (customer.isVIP())  // Auto Unboxing
    {
        handleNow(customer);
    }
    else
    {  
        sayHandlingNowButQueueForTomorrow(customer);
    }
}

或者：

public void handleCustomer(Customer customer)
{
    if (customer.isVIP().booleanValue()) // Explicit unboxing
    {
        handleNow(customer);
    }
    else
    {  
        sayHandlingNowButQueueForTomorrow(customer);
    }
}

推荐答案

否它们之间的区别，你可以在字节码中验证它：

No difference between them, you can verify it in the bytecode:

public class ImplicitTest {
    public static void main(String[] args) {
        Boolean b = true; 
        boolean i = b;
        boolean e = b.booleanValue();
    }
}

运行 javap 看看它是什么编译为：

Run javap to see what it compiles to:

javap -c ImplicitTest

以下是输出：

Compiled from "ImplicitTest.java"
public class ImplicitTest extends java.lang.Object{
public ImplicitTest();
  Code:
   0:   aload_0
   1:   invokespecial   #1; //Method java/lang/Object."<init>":()V
   4:   return

public static void main(java.lang.String[]);
  Code:
   0:   iconst_1
   1:   invokestatic    #2; //Method java/lang/Boolean.valueOf:(Z)Ljava/lang/Boolean;
   4:   astore_1
   5:   aload_1
   6:   invokevirtual   #3; //Method java/lang/Boolean.booleanValue:()Z
   9:   istore_2
   10:  aload_1
   11:  invokevirtual   #3; //Method java/lang/Boolean.booleanValue:()Z
   14:  istore_3
   15:  return

}

如您所见 - 第5,6,9行（隐式）与10,11,14（显式）相同。

As you can see - lines 5,6,9 (implicit) are the same as 10, 11, 14 (explicit).

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