在Java中使用完全限定名称和导入之间的区别

问题描述：

在Java中，在性能，内存，编译时间等方面，使用内联导入"(全限定名)和普通导入是否有任何区别?

Are there any differences using an "inline import" (a fully qualified name) and normal import in terms of performance, memory, compile-time, etc. in Java?

chooser.setCurrentDirectory(new java.io.File("."));

和

import java.io.File;
...
   chooser.setCurrentDirectory(new File("."));

答

您应该关注的主要内容是可读性.我发现第二个更具可读性.

The main thing you should focus in is readability. I find the second one more readable.

在极少数情况下，我更喜欢第二种方法.让我们考虑以下情形:由于某种原因，我编写了一个类并将其命名为File.我输入了File file = new File(...)，IDE为我自动导入了java.io.File.但是我不需要那种对象，我需要 my File类.因此，与导入正确的类相比，我更喜欢内联导入它，只是其他用户不会与Java的File类混淆.

In rare cases, I prefer the second approach. Let's consider the following scenario: For some reason, I wrote a class and named it File. I typed File file = new File(...) and my IDE auto-imported the java.io.File for me. But I don't want that kind of object, I want my File class. So instead of importing the correct class, I prefer inline-import it, just that other users won't get confused with the Java's File class.

关于性能，它们完全相同，这就是证明-

Regarding the performance, they're exactly the same, and here's the proof -

这是为第一个代码段生成的字节码:

This is the bytecode generated for the first snippet:

public class java8.tests.General {
  public java8.tests.General();
    Code:
       0: aload_0
       1: invokespecial #1                  // Method java/lang/Object."<init>":()V
       4: return

  public static void main(java.lang.String[]);
    Code:
       0: new           #2                  // class javax/swing/JFileChooser
       3: dup
       4: invokespecial #3                  // Method javax/swing/JFileChooser."<init>":()V
       7: astore_1
       8: aload_1
       9: new           #4                  // class java/io/File
      12: dup
      13: ldc           #5                  // String .
      15: invokespecial #6                  // Method java/io/File."<init>":(Ljava/lang/String;)V
      18: invokevirtual #7                  // Method javax/swing/JFileChooser.setCurrentDirectory:(Ljava/io/File;)V
      21: return
}

这是第二个字节码:

public class java8.tests.General {
  public java8.tests.General();
    Code:
       0: aload_0
       1: invokespecial #1                  // Method java/lang/Object."<init>":()V
       4: return

  public static void main(java.lang.String[]);
    Code:
       0: new           #2                  // class javax/swing/JFileChooser
       3: dup
       4: invokespecial #3                  // Method javax/swing/JFileChooser."<init>":()V
       7: astore_1
       8: aload_1
       9: new           #4                  // class java/io/File
      12: dup
      13: ldc           #5                  // String .
      15: invokespecial #6                  // Method java/io/File."<init>":(Ljava/lang/String;)V
      18: invokevirtual #7                  // Method javax/swing/JFileChooser.setCurrentDirectory:(Ljava/io/File;)V
      21: return
}

在Java中使用完全限定名称和导入之间的区别

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