Follow Javac code to clarify matters bytecode

　　Foreword　　

　　This article is a follow Nuggets booklet of them are "JVM bytecode from entry to the master" written exercises.

　　problem

　　Question one:

　　We have the following code:

 1 package com.sun.tools.javac;
 2 
 3 /**
 4  * @author TY
 5  */
 6 public class Foo {
 7 
 8     public static void foo() {
 9         int a = 0;
10         int b = 6;
11         int c = 130;
12         int d = 33000;
13     }
14 
15 }

　　Very simple piece of code, it seems there is no place worthy of discussion, but the code will see the next byte code with javap:

　　Can be seen for different variable definitions, bytecode instructions are different, though are integers. . . Why do? Simple analysis can be learned, and it is

It has declared value relationship, different bytecode instructions for different size ranges. But our ideas on how to verify it? I believe many people are not aware of. We will be mentioned below how to verify

our thoughts.

　　Question two:

　　Note that the following code:

 1 package com.sun.tools.javac;
 2 
 3 /**
 4  * @author TY
 5  */
 6 public class Switch {
 7 
 8     public static void foo() {
 9         int a = 0;
10         switch (a) {
11             case 0:
12                 System.out.println("#0");
13                 break;
14             case 1:
15                 System.out.println("#1");
16                 break;
17             default:
18                 System.out.println("default");
19                 break;
20         }
21     }
22 
23 }

　　Swtich ... case for some simple logic, there is no problem watching, take a look at the byte code:

　　See above bytecode, using looupswitch, and we know that, switch ... case statement, there are two underlying command: tableswitch and looupswitch, before I

When studying just know tableswtich case value applies to a relatively compact case and is suitable for case lookupswitch value relatively sparse. But the above code

case values are 0 and 1 ,,, this this this, sort of a kip sparse, so why should lookupswitch without tableswtich it?

　　Source Javac

　　We know that the Java code is compiled into byte code command is Javac, so on the above issues, we should look for answers in Javac source inside.

　　First, download the source code Javac, here I offer them are the address provided: javac-Source-code-Reading

　　After downloading a good open with IDEA: