Is there any change in the constant pool entires with JDK1.4?

Question

Hi,
Here is my simple java class,
class Base
String manuf = "MRF";
class Derived extends Base
Derived() {
manuf = "ABC";
After compiling this class with JDK 1.3 and JDK1.4, i could see the difference in constant pool entries
so please let me know more about these cahnges.
P.S. : written a java program TClass.java to browse the constant pool entries.
i.e if compiled with JDK1.3 , constant pool entries looks as follows,
E:\bugs\jdk1.4\pramila>java TClass E:\bugs\jdk1.4\pramila\Derived.class
There are 21 + 1 entries in the Constant Pool:
Index Tag Reference(s)/Value(s)
1 10 5 15
2 8 16
3 9 5 17
4 7 18
5 7 19
6 1 <init>
7 1 ()V
8 1 Code
9 1 LineNumberTable
10 1 LocalVariableTable
11 1 this
12 1 LDerived;
13 1 SourceFile
14 1 Test.java
15 12 6 7
16 1 ABC
17 12 20 21
18 1 Derived
19 1 Base
20 1 manuf
21 1 Ljava/lang/String;
There are 1 methods:
Code array in method <init> of length 11 starting at byte 231.
If compiled with JDK1.4 constant pool entries looks as follows,
E:\bugs\jdk1.4\pramila>java TClass E:\bugs\jdk1.4\pramila\Derived.class
There are 21 + 1 entries in the Constant Pool:
Index Tag Reference(s)/Value(s)
1 10 5 15
2 8 16
3 9 4 17
4 7 18
5 7 19
6 1 <init>
7 1 ()V
8 1 Code
9 1 LineNumberTable
10 1 LocalVariableTable
11 1 this
12 1 LDerived;
13 1 SourceFile
14 1 Test.java
15 12 6 7
16 1 ABC
17 12 20 21
18 1 Derived
19 1 Base
20 1 manuf
21 1 Ljava/lang/String;
There are 1 methods:
Code array in method <init> of length 11 starting at byte 231.
There is a change in the index 3 can be noticed.
i.e
with JDK1.3 it is "3 9 5 17"
with JDK1.4 it is "3 9 4 17"
Thanks in advance.
Pramila

Answer 1

javac v1.4 emits by default Java 1.2 compatible .class files while all javac implementations since between 1.1.0 and 1.3.1 emit byte default Java 1.1 .class files.
Check to see what effect using the -target option in javac to get the two versions to produce Java 1.1, 1.2, or 1.3 .class files.
Chuck