受教于《深入理解Java虚拟机》周志明著
直接看ByteCode文件会累死的,我们可以用JDK附带的javap -verbose A.class 来生成可读的信息.
下面就举个例子,看下这类信息中的Constant Pool部分
package pool;
public class PlayConstant {
private static final int DEFAULT_PLAYER_COUNT = 55;
private String gameName;
public Long getMoney(int playerCount) {
long money = 10 * playerCount;
return money;
}
}
一起来分析一下它的Constant Pool:
const #1 = class #2; // pool/PlayConstant --#2意思是它的值在Pool中的第#2个位置 const #2 = Asciz pool/PlayConstant; const #3 = class #4; // java/lang/Object --父类 const #4 = Asciz java/lang/Object; const #5 = Asciz DEFAULT_PLAYER_COUNT; --常量名 const #6 = Asciz I; --常量类型,I意思是int const #7 = Asciz ConstantValue; --将为常量设值 const #8 = int 55; --常量值为55 const #9 = Asciz gameName; --成员变量名 const #10 = Asciz Ljava/lang/String;; --成员变量类型,凡是对象都会在类型前加个"Ｌ" const #11 = Asciz <init>; --构造方法 const #12 = Asciz ()V; --构造方法为void const #13 = Asciz Code; const #14 = Method #3.#15; // java/lang/Object."<init>":()V --所调用的父类构造方法的签名 const #15 = NameAndType #11:#12;// "<init>":()V const #16 = Asciz LineNumberTable; --编译时记录了Line Number const #17 = Asciz LocalVariableTable; --编译时记录了变量名 const #18 = Asciz this; --this_class const #19 = Asciz Lpool/PlayConstant;; --本类的全名 const #20 = Asciz getMoney; --成员方法名 const #21 = Asciz (I)Ljava/lang/Long;; --成员方法返回类型 const #22 = Method #23.#25; // java/lang/Long.valueOf(J)Ljava/lang/Long; const #23 = class #24; // java/lang/Long const #24 = Asciz java/lang/Long; const #25 = NameAndType #26:#27;// valueOf:(J)Ljava/lang/Long; const #26 = Asciz valueOf; const #27 = Asciz (J)Ljava/lang/Long;; --方法的参数的类型 const #28 = Asciz playerCount; --方法的参数名 const #29 = Asciz money; --方法里面的局部变量名 const #30 = Asciz J; --局部变量类型: long const #31 = Asciz SourceFile; --编译时记录了源文件名 const #32 = Asciz PlayConstant.java; --源文件名