如果我有以下两个类：
// Base.java
public abstract class Base<T> {
abstract void method(T t);
}
和
// Derived.java
public class Derived extends Base<Number> {
@Deprecated
void method(Number n) {}
}
然后我使用javac Base.java Derived.java编译它们,然后使用javap -v Derived.如果我使用Java 7,我得到
public class Derived extends Base<java.lang.Number>
Signature: #17 // LBase<Ljava/lang/Number;>;
SourceFile: "Derived.java"
minor version: 0
major version: 51
flags: ACC_PUBLIC,ACC_SUPER
Constant pool:
#1 = Methodref #5.#20 // Base."<init>":()V
#2 = Class #21 // java/lang/Number
#3 = Methodref #4.#22 // Derived.method:(Ljava/lang/Number;)V
#4 = Class #23 // Derived
#5 = Class #24 // Base
#6 = Utf8 <init>
#7 = Utf8 ()V
#8 = Utf8 Code
#9 = Utf8 LineNumberTable
#10 = Utf8 method
#11 = Utf8 (Ljava/lang/Number;)V
#12 = Utf8 Deprecated
#13 = Utf8 RuntimeVisibleAnnotations
#14 = Utf8 Ljava/lang/Deprecated;
#15 = Utf8 (Ljava/lang/Object;)V
#16 = Utf8 Signature
#17 = Utf8 LBase<Ljava/lang/Number;>;
#18 = Utf8 SourceFile
#19 = Utf8 Derived.java
#20 = NameAndType #6:#7 // "<init>":()V
#21 = Utf8 java/lang/Number
#22 = NameAndType #10:#11 // method:(Ljava/lang/Number;)V
#23 = Utf8 Derived
#24 = Utf8 Base
{
public Derived();
flags: ACC_PUBLIC
Code:
stack=1,locals=1,args_size=1
0: aload_0
1: invokespecial #1 // Method Base."<init>":()V
4: return
LineNumberTable:
line 1: 0
void method(java.lang.Number);
flags:
Code:
stack=0,locals=2,args_size=2
0: return
LineNumberTable:
line 7: 0
Deprecated: true
RuntimeVisibleAnnotations:
0: #14()
void method(java.lang.Object);
flags: ACC_BRIDGE,ACC_SYNTHETIC
Code:
stack=2,args_size=2
0: aload_0
1: aload_1
2: checkcast #2 // class java/lang/Number
5: invokevirtual #3 // Method method:(Ljava/lang/Number;)V
8: return
LineNumberTable:
line 1: 0
}
如果我用Java 8做同样的事情,我会得到
public class Derived extends Base<java.lang.Number>
minor version: 0
major version: 52
flags: ACC_PUBLIC,ACC_SUPER
Constant pool:
#1 = Methodref #5.#20 // Base."<init>":()V
#2 = Class #21 // java/lang/Number
#3 = Methodref #4.#22 // Derived.method:(Ljava/lang/Number;)V
#4 = Class #23 // Derived
#5 = Class #24 // Base
#6 = Utf8 <init>
#7 = Utf8 ()V
#8 = Utf8 Code
#9 = Utf8 LineNumberTable
#10 = Utf8 method
#11 = Utf8 (Ljava/lang/Number;)V
#12 = Utf8 Deprecated
#13 = Utf8 RuntimeVisibleAnnotations
#14 = Utf8 Ljava/lang/Deprecated;
#15 = Utf8 (Ljava/lang/Object;)V
#16 = Utf8 Signature
#17 = Utf8 LBase<Ljava/lang/Number;>;
#18 = Utf8 SourceFile
#19 = Utf8 Derived.java
#20 = NameAndType #6:#7 // "<init>":()V
#21 = Utf8 java/lang/Number
#22 = NameAndType #10:#11 // method:(Ljava/lang/Number;)V
#23 = Utf8 Derived
#24 = Utf8 Base
{
public Derived();
descriptor: ()V
flags: ACC_PUBLIC
Code:
stack=1,args_size=1
0: aload_0
1: invokespecial #1 // Method Base."<init>":()V
4: return
LineNumberTable:
line 1: 0
void method(java.lang.Number);
descriptor: (Ljava/lang/Number;)V
flags:
Code:
stack=0,args_size=2
0: return
LineNumberTable:
line 5: 0
Deprecated: true
RuntimeVisibleAnnotations:
0: #14()
void method(java.lang.Object);
descriptor: (Ljava/lang/Object;)V
flags: ACC_BRIDGE,args_size=2
0: aload_0
1: aload_1
2: checkcast #2 // class java/lang/Number
5: invokevirtual #3 // Method method:(Ljava/lang/Number;)V
8: return
LineNumberTable:
line 1: 0
RuntimeVisibleAnnotations:
0: #14()
}
Signature: #17 // LBase<Ljava/lang/Number;>;
SourceFile: "Derived.java"
这里要注意的是,在Java 7版本中不存在的Java 8版本中的void方法(java.lang.Object)存根上有一个注释.这不仅仅是javap错误 – 如果您使用反射来检查运行时存在的注释,则Java 7版本仅在void方法(java.lang.Number)上具有注释,并且Java 8版本都具有这两个注释.这是怎么回事？
解决方法
这是因为它是固定的,因为这种行为似乎更加一致.有关详细信息,请参阅
JDK-6695379问题.而且这不仅仅是Java 8,它也被转载到Java 7u80：
C:\Test>"C:\Program Files\Java\jdk1.7.0_79\bin\javac.exe" Derived.java C:\Test>javap -v Derived.class >javac7_79 C:\Test>"C:\Program Files\Java\jdk1.7.0_80\bin\javac.exe" Derived.java C:\Test>javap -v Derived.class >javac7_80 C:\Test>diff javac7_79 javac7_80 2,3c2,3 < Last modified 18.05.2015; size 484 bytes < MD5 checksum bd5e729c8eda30f72f3dc5301fa9bfc2 --- > Last modified 18.05.2015; size 496 bytes > MD5 checksum 728d9e30b9aab2381e711b3edd008000 69a70,71 > RuntimeVisibleAnnotations: > 0: #14()
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