LetExpr表达式解读

Integer a = 0;
a++;

　　

举个例子，如下：

package com.test19;

public class BugReport<T> {

	private T n;

	public void error() {
		BugReport<Integer> val = new BugReport<Integer>();
		val.n = 0;

		Integer.toString(val.n++);
	}

	public static void main(String[] args) {
		BugReport.class.getMethods();
	}
}　　

经过反编译后如下：

package com.test19;

public class BugReport<T> {
    private T n;

    public BugReport() {
    }

    public void error() {
        BugReport var1 = new BugReport();
        var1.n = Integer.valueOf(0);
        Integer var3 = (Integer)var1.n;
        Object var4 = var1.n = Integer.valueOf(((Integer)var1.n).intValue() + 1);
        Integer.toString(var3.intValue());
    }

    public static void main(String[] var0) {
        BugReport.class.getMethods();
    }
}

生成的class文件格式如下：

Classfile /C:/BugReport.class
  Last modified 2018-7-22; size 741 bytes
  MD5 checksum 3c3412b5bb98381c1e3035573f40b89c
  Compiled from "BugReport.java"
public class com.test19.BugReport<T extends java.lang.Object> extends java.lang.Object
  Signature: #22                          // <T:Ljava/lang/Object;>Ljava/lang/Object;
  SourceFile: "BugReport.java"
  minor version: 0
  major version: 51
  flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
   #1 = Methodref          #10.#25        //  java/lang/Object."<init>":()V
   #2 = Class              #26            //  com/test19/BugReport
   #3 = Methodref          #2.#25         //  com/test19/BugReport."<init>":()V
   #4 = Methodref          #6.#27         //  java/lang/Integer.valueOf:(I)Ljava/lang/Integer;
   #5 = Fieldref           #2.#28         //  com/test19/BugReport.n:Ljava/lang/Object;
   #6 = Class              #29            //  java/lang/Integer
   #7 = Methodref          #6.#30         //  java/lang/Integer.intValue:()I
   #8 = Methodref          #6.#31         //  java/lang/Integer.toString:(I)Ljava/lang/String;
   #9 = Methodref          #32.#33        //  java/lang/Class.getMethods:()[Ljava/lang/reflect/Method;
  #10 = Class              #34            //  java/lang/Object
  #11 = Utf8               n
  #12 = Utf8               Ljava/lang/Object;
  #13 = Utf8               Signature
  #14 = Utf8               TT;
  #15 = Utf8               <init>
  #16 = Utf8               ()V
  #17 = Utf8               Code
  #18 = Utf8               LineNumberTable
  #19 = Utf8               error
  #20 = Utf8               main
  #21 = Utf8               ([Ljava/lang/String;)V
  #22 = Utf8               <T:Ljava/lang/Object;>Ljava/lang/Object;
  #23 = Utf8               SourceFile
  #24 = Utf8               BugReport.java
  #25 = NameAndType        #15:#16        //  "<init>":()V
  #26 = Utf8               com/test19/BugReport
  #27 = NameAndType        #35:#36        //  valueOf:(I)Ljava/lang/Integer;
  #28 = NameAndType        #11:#12        //  n:Ljava/lang/Object;
  #29 = Utf8               java/lang/Integer
  #30 = NameAndType        #37:#38        //  intValue:()I
  #31 = NameAndType        #39:#40        //  toString:(I)Ljava/lang/String;
  #32 = Class              #41            //  java/lang/Class
  #33 = NameAndType        #42:#43        //  getMethods:()[Ljava/lang/reflect/Method;
  #34 = Utf8               java/lang/Object
  #35 = Utf8               valueOf
  #36 = Utf8               (I)Ljava/lang/Integer;
  #37 = Utf8               intValue
  #38 = Utf8               ()I
  #39 = Utf8               toString
  #40 = Utf8               (I)Ljava/lang/String;
  #41 = Utf8               java/lang/Class
  #42 = Utf8               getMethods
  #43 = Utf8               ()[Ljava/lang/reflect/Method;
{
  public com.test19.BugReport();
    flags: ACC_PUBLIC
    Code:
      stack=1, locals=1, args_size=1
         0: aload_0
         1: invokespecial #1                  // Method java/lang/Object."<init>":()V
         4: return
      LineNumberTable:
        line 3: 0

  public void error();
    flags: ACC_PUBLIC
    Code:
      stack=3, locals=5, args_size=1
         0: new           #2                  // class com/test19/BugReport
         3: dup
         4: invokespecial #3                  // Method "<init>":()V
         7: astore_1
         8: aload_1
         9: iconst_0
        10: invokestatic  #4                  // Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;
        13: putfield      #5                  // Field n:Ljava/lang/Object;
        16: aload_1
        17: astore_2
        18: aload_2
        19: getfield      #5                  // Field n:Ljava/lang/Object;
        22: checkcast     #6                  // class java/lang/Integer
        25: astore_3
        26: aload_2
        27: aload_2
        28: getfield      #5                  // Field n:Ljava/lang/Object;
        31: checkcast     #6                  // class java/lang/Integer
        34: invokevirtual #7                  // Method java/lang/Integer.intValue:()I
        37: iconst_1
        38: iadd
        39: invokestatic  #4                  // Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;
        42: dup_x1
        43: putfield      #5                  // Field n:Ljava/lang/Object;
        46: astore        4
        48: aload_3
        49: invokevirtual #7                  // Method java/lang/Integer.intValue:()I
        52: invokestatic  #8                  // Method java/lang/Integer.toString:(I)Ljava/lang/String;
        55: pop
        56: return
      LineNumberTable:
        line 8: 0
        line 9: 8
        line 10: 16
        line 11: 56

  public static void main(java.lang.String[]);
    flags: ACC_PUBLIC, ACC_STATIC
    Code:
      stack=1, locals=1, args_size=1
         0: ldc_w         #2                  // class com/test19/BugReport
         3: invokevirtual #9                  // Method java/lang/Class.getMethods:()[Ljava/lang/reflect/Method;
         6: pop
         7: return
      LineNumberTable:
        line 14: 0
        line 15: 7
}