Test 1:
純粹宣告一個public的類別
string_test.java
public class string_test{ }
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java string_test
Error: Main method not found in class string_test, please define the main method as:
public static void main(String[] args)
or a JavaFX application class must extend javafx.application.Application
執行錯誤，因為沒有程式進入點 main
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javap string_test
Classfile /c:/../string_test.class
Last modified 2016/5/3; size 196 bytes
MD5 checksum ..
Compiled from "string_test.java"
public class string_test
minor version: 0
major version: 52
flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
#1 = Methodref #3.#10 // java/lang/Object."<init>":()V
#2 = Class #11 // string_test
#3 = Class #12 // java/lang/Object
#4 = Utf8 <init>
#5 = Utf8 ()V
#6 = Utf8 Code
#7 = Utf8 LineNumberTable
#8 = Utf8 SourceFile
#9 = Utf8 string_test.java
#10 = NameAndType #4:#5 // "<init>":()V
#11 = Utf8 string_test
#12 = Utf8 java/lang/Object
{
public string_test();
descriptor: ()V
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 1: 0
}
SourceFile: "string_test.java"
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Test 2:
加入了程式進入點函式，詳細內容請查其他網站。
string_test.java
public class string_test{
public static void main(String args[]){ }
}
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java string_test
沒有執行錯誤，正常執行。
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javap string_test
多了一個函式，函式是個有輸入參數 args，是個 String[] 字串陣列。
在 class file 中，會以函式來區分，所以可以看到多了一個區域來存放 main。
Classfile /c:/../string_test.class
Last modified 2016/5/3; size 267 bytes
MD5 checksum ..
Compiled from "string_test.java"
public class string_test
minor version: 0
major version: 52
flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
#1 = Methodref #3.#12 // java/lang/Object."<init>":()V
#2 = Class #13 // string_test
#3 = Class #14 // java/lang/Object
#4 = Utf8 <init>
#5 = Utf8 ()V
#6 = Utf8 Code
#7 = Utf8 LineNumberTable
#8 = Utf8 main
#9 = Utf8 ([Ljava/lang/String;)V
#10 = Utf8 SourceFile
#11 = Utf8 string_test.java
#12 = NameAndType #4:#5 // "<init>":()V
#13 = Utf8 string_test
#14 = Utf8 java/lang/Object
{
public string_test();
descriptor: ()V
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 1: 0
public static void main(java.lang.String[]);
descriptor: ([Ljava/lang/String;)V
flags: ACC_PUBLIC, ACC_STATIC
Code:
stack=0, locals=1, args_size=1
0: return
LineNumberTable:
line 6: 0
}
SourceFile: "string_test.java"
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Test 3:
多宣告了一個字串參數，但是不給他值。
string_test.java
public class string_test{
public static void main(String args[]){ String s; }
}
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java string_test
沒有執行錯誤，正常執行。
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javap string_test
因為多宣告了一個參數，所以Local variable會多 1。
.
.
public static void main(java.lang.String[]);
descriptor: ([Ljava/lang/String;)V
flags: ACC_PUBLIC, ACC_STATIC
Code:
stack=0, locals=2, args_size=1
0: return
LineNumberTable:
line 6: 0
}
SourceFile: "string_test.java"
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string_test.java
給字串 s 值 "s";
public class string_test{
public static void main(String args[]){ String s = "Y"; }
}
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java string_test
沒有執行錯誤，正常執行。
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javap string_test
由opcode code 可以看到，現在會先由 constant pool 中將字串訊息引入，
在將他用 ASTORE 來和 local variable 位置 1 的值連結。
LDC - Push item from constant pool.
| ASTORE - Store reference into local variable |
Classfile /c:/../string_test.class
Last modified 2016/5/3; size 281 bytes
MD5 checksum ..
Compiled from "string_test.java"
public class string_test
minor version: 0
major version: 52
flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
#1 = Methodref #4.#13 // java/lang/Object."<init>":()V
#2 = String #14 // Y
#3 = Class #15 // string_test
#4 = Class #16 // java/lang/Object
#5 = Utf8 <init>
#6 = Utf8 ()V
#7 = Utf8 Code
#8 = Utf8 LineNumberTable
#9 = Utf8 main
#10 = Utf8 ([Ljava/lang/String;)V
#11 = Utf8 SourceFile
#12 = Utf8 string_test.java
#13 = NameAndType #5:#6 // "<init>":()V
#14 = Utf8 Y
#15 = Utf8 string_test
#16 = Utf8 java/lang/Object
{
public string_test();
descriptor: ()V
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 1: 0
public static void main(java.lang.String[]);
descriptor: ([Ljava/lang/String;)V
flags: ACC_PUBLIC, ACC_STATIC
Code:
stack=1, locals=2, args_size=1
0: ldc #2 // String Y
2: astore_1
3: return
LineNumberTable:
line 3: 0
line 6: 3
}
SourceFile: "string_test.java"
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string_test.java
public class string_test{
public static void main(String args[]){
String s;
/*String s1 = "s1";
System.out.println(s);*/
}
}
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java string_test
沒有執行錯誤，正常執行。
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javap string_test
多了一個函式，函式是
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string_test.java
public class string_test{
public static void main(String args[]){
String s;
/*String s1 = "s1";
System.out.println(s);*/
}
}
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java string_test
沒有執行錯誤，正常執行。
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javap string_test
多了一個函式，函式是
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string_test.java
public class string_test{
public static void main(String args[]){
String s;
/*String s1 = "s1";
System.out.println(s);*/
}
}
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java string_test
沒有執行錯誤，正常執行。
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javap string_test
多了一個函式，函式是
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string_test.java
public class string_test{
public static void main(String args[]){
String s;
/*String s1 = "s1";
System.out.println(s);*/
}
}
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java string_test
沒有執行錯誤，正常執行。
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javap string_test
多了一個函式，函式是
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