泛型

类型擦除

今天同事遇到个问题，好好看了下泛型这块

• java的泛型比较重要的一点是类型擦除。避免生成多个class文件
  ** 例子 **

(忽略代码规范
public class testTypeErase {
 
 private class Base {
  
  protected <T> T test(TypeRefer typeRefer) {
   T t = null;
   return t;
  }
 }
 
 private class TypeRefer<T> {
  //private final Class<T> type;

  T value;
      public TypeRefer(T value) {
       this.value = value;
      }

      public void getValue() {
       System.out.println((String)value);
      }
 }
 
 private class Child<T> extends Base {
  private T value;
  public Child(T value) {
   this.value = value;
  }
  public T testChild() {
   TypeRefer ty = new TypeRefer<T>(value);
   ty.getValue();
   T t = null;
   return t;
  }
 }

** javap看字节码头 **

class test.zk.generic.testTypeErase$Child<T> extends test.zk.generic.testTypeErase$Base {
  final test.zk.generic.testTypeErase this$0;

  public test.zk.generic.testTypeErase$Child(T);
    Code:
       0: aload_0
       1: aload_1
       2: putfield      #15                 // Field this$0:Ltest/zk/generic/testTypeErase;
       5: aload_0
       6: aload_1
       7: aconst_null
       8: invokespecial #17                 // Method test/zk/generic/testTypeErase$Base."<init>":(Ltest/zk/generic/testTypeErase;Ltest/zk/generic/testTypeErase$Base;)V
      11: aload_0
      12: aload_2
      13: putfield      #20                 // Field value:Ljava/lang/Object;
      16: return

  public T testChild();
    Code:
       0: new           #31                 // class test/zk/generic/testTypeErase$TypeRefer
       3: dup
       4: aload_0
       5: getfield      #15                 // Field this$0:Ltest/zk/generic/testTypeErase;
       8: aload_0
       9: getfield      #20                 // Field value:Ljava/lang/Object;
      12: invokespecial #33                 // Method test/zk/generic/testTypeErase$TypeRefer."<init>":(Ltest/zk/generic/testTypeErase;Ljava/lang/Object;)V
      15: astore_1
      16: aload_1
      17: invokevirtual #35                 // Method test/zk/generic/testTypeErase$TypeRefer.getValue:()V
      20: aconst_null
      21: astore_2
      22: aload_2
      23: areturn

参考

泛型 oracle
泛型 类型擦除