Java泛型类型擦除字节码 [英] Java Generics Type Erasure byte code

问题描述

根据关于擦除泛型类型的java文档 ，

考虑以下泛型类，它表示一个单链表中的节点：$ b​​
$ b

  public class Node< T> {
 
私人T数据; 
私人节点< T>下一个; 
 
 public Node（T data，Node< T> next）} 
 this.data = data; 
 this.next = next; 
} 
 
 public T getData（）{return data; } 
 // ... 
} 
  

因为类型参数 T 是无界的，Java编译器用 Object 替换它：

  public class节点{
 
私人对象数据; 
下一个私人节点; 
 
 public Node（Object data，Node next）{
 this.data = data; 
 this.next = next; 
} 
 
 public Object getData（）{return data; } 
 // ... 
} 
  

但是用Java 1.7编译后.0_11，当我用任何反编译器打开它时，我可以看到与源代码相同的代码。

  public class Node< T> ; 
 {
私人T数据; 
私人节点< T>下一个; 
 
 public Node（T paramT，Node< T> paramNode）
 {
 this.data = paramT; 
 this.next = paramNode; 
} 
 
 public T getData（）
 {
 return this.data; 
 
 
 
 
 
 
 
如果在编译时应用了Type-Erasure，那么字节代码不得包含如上所示的通用信息。请澄清我。
 
 
 
 注意：我使用 JD-GUI 作为反编译器来分析字节码
解决方案
关于代码本身的信息，比如泛型（或者变量名） - 这并不意味着它可以被JVM使用。 
 
 
类的反汇编字节码如下所示（你可以用 javap -c Node.class ）看到它： 
 
 
 公共类节点< T> {
公共节点（T，节点< T>）; 
代码：
 0：aload_0 
 1：invokespecial＃1 //方法java / lang / Object。< init>:(）V 
 4：aload_0 
 5：aload_1 
 6：putfield＃2 //字段数据：Ljava / lang / Object; 
 9：aload_0 
 10：aload_2 
 11：putfield＃3 // Field next：LNode; 
 14：返回
 
 public T getData（）; 
代码：
 0：aload_0 
 1：getfield＃2 //字段数据：Ljava / lang / Object; 
 4：areturn 
} 
  
你可以看到方法和参数是通用的类型在那里，但由于擦除过程，代码本身就像预期的那样引用Object。
 
As per the java documentation on Erasure of Generic Types, 

Consider the following generic class that represents a node in a singly linked list:
public class Node<T> {

    private T data;
    private Node<T> next;

    public Node(T data, Node<T> next) }
        this.data = data;
        this.next = next;
    }

    public T getData() { return data; }
    // ...
}
Because the type parameter T is unbounded, the Java compiler replaces it with Object:
public class Node {

    private Object data;
    private Node next;

    public Node(Object data, Node next) {
        this.data = data;
        this.next = next;
    }

    public Object getData() { return data; }
    // ...
}
But after compilation with Java 1.7.0_11, when I opened it with any decompiler I can see the same code as like source code.
public class Node<T>
{
  private T data;
  private Node<T> next;

  public Node(T paramT, Node<T> paramNode)
  {
    this.data = paramT;
    this.next = paramNode;
  }

  public T getData()
  {
    return this.data;
  }
}
If Type-Erasure applied at compile then the byte code must not contain Generic information as shown above. Kindly clarify me.

NOTE: I am using JD-GUI as a decompiler to analyze the byte code
解决方案
The bytecode contains meta information about the code itself, such as generic types (or variable names) - it does not mean it's useable by the JVM.

The disassembled bytecode of your class looks like below (you can see it with javap -c Node.class):
public class Node<T> {
  public Node(T, Node<T>);
    Code:
       0: aload_0
       1: invokespecial #1                  // Method java/lang/Object."<init>":()V
       4: aload_0
       5: aload_1
       6: putfield      #2                  // Field data:Ljava/lang/Object;
       9: aload_0
      10: aload_2
      11: putfield      #3                  // Field next:LNode;
      14: return

  public T getData();
    Code:
       0: aload_0
       1: getfield      #2                  // Field data:Ljava/lang/Object;
       4: areturn
}
You can see that the methods and arguments generic types are there but the code itself refers to Object as expected due to the erasure process.

                        
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