tried to recompile oldest java software

Question

I am not an experienced programmer and I know very little java.

I have a small 10 year old java software compiled with java1.5. Obviously I don't have the source code. This software has a small bug, so I used a java decompiler and found the bug. The solution is very simple but I am having difficulty recompiling the class. I am using java1.5.0_12 to recompile.

Unfortunately it seems that the compiler is encountering some errors in the code.

it/cp/pacm/dbsync/Synchronizer.java:234: possible loss of precision
found   : int
required: char
/*  287 */       c = Integer.parseInt(strLdapPort);

the code is

/*      */     char c;
...
/*  287 */       c = Integer.parseInt(strLdapPort);

I fixed that with casting.

/*  287 */       c = (char)Integer.parseInt(strLdapPort);

But there remains a problem that I cannot solve

# javac -cp ../software.jar it/cp/pacm/dbsync/Synchronizer.java

software.jar is the whole package

it/cp/pacm/dbsync/Synchronizer.java:415: cannot find symbol
symbol  : class E
location: class it.cp.pacm.dbsync.Synchronizer
/*  497 */       for (Iterator<E> iterator = removedEntries.keySet().iterator(); iterator.hasNext(); ) {
                               ^
it/cp/pacm/dbsync/Synchronizer.java:463: incompatible types
found   : java.util.Iterator<java.lang.Object>
required: java.util.Iterator<java.lang.String>
/*  552 */     for (Iterator<String> iterator1 = newAttributes.keySet().iterator(); iterator1.hasNext(); ) {
                                                                                ^
it/cp/pacm/dbsync/Synchronizer.java:475: incompatible types
found   : java.util.Iterator<java.lang.Object>
required: java.util.Iterator<java.lang.String>
/*  571 */     for (Iterator<String> i = oldAttributes.keySet().iterator(); i.hasNext(); ) {
                                                                        ^
it/cp/pacm/dbsync/Synchronizer.java:673: unexpected type
found   : byte
required: reference
/*  816 */     Arrays.sort(values, (Comparator<? super byte>)new ByteArrayComparator());
                                                       ^
Note: it/cp/pacm/dbsync/Synchronizer.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
4 errors

I don't know where the class E was defined.

is there any option to ignore these errors?

using jdk1.5.0_11 it not start to build:

Error occurred during initialization of VM
java/lang/NoClassDefFoundError: java/lang/Object

Also the directory contains some other unknown class file

Synchronizer$DEFAULTS.class
Synchronizer$DNOrder.class
Synchronizer$EntryOrder.class
Synchronizer$SETTINGS.class
Synchronizer.class

Thank you

Answer 1

You should know a little bit more of Java before attempting to decompile/recompile: especially since decompiler may fail in the process and produce a code that seems valid but is in fact invalid. It should be used to analyze rather than to fix existing code.

Also, different decompiler produce different result: the Eclipse Enhanced Class Decompiler use several type of decompiler.

For your errors:

it/cp/pacm/dbsync/Synchronizer.java:415: cannot find symbol
symbol  : class E
location: class it.cp.pacm.dbsync.Synchronizer
/*  497 */       for (Iterator<E> iterator = removedEntries.keySet().iterator(); iterator.hasNext(); ) {

This error involve a generic type E (given the name; not much I can infer from the source code here).

You should look at the removedEntries which I assume to be a Map: the decompiler might have left it as Map rather than Map<E, Object>. And the generic type E is not defined in the parent context (method, class):

<E> void foobar(Map<E, ?> removedEntries) {
  for (Iterator<E> iterator = removedEntries.keySet().iterator(); iterator.hasNext(); ) {
    // ...
  }
}

The code above would probably compile: the generic type E is declared.

it/cp/pacm/dbsync/Synchronizer.java:463: incompatible types
found   : java.util.Iterator<java.lang.Object>
required: java.util.Iterator<java.lang.String>
/*  552 */     for (Iterator<String> iterator1 = newAttributes.keySet().iterator(); iterator1.hasNext(); ) {

Same problem, not the same cause: your decompiler probably is not capable of infering the types of generic in generic types. Eg: newAttributes is probably defined just as Map but it should be Map<String, ?>.

it/cp/pacm/dbsync/Synchronizer.java:673: unexpected type
found   : byte
required: reference
/*  816 */     Arrays.sort(values, (Comparator<? super byte>)new ByteArrayComparator());

Easy: use Byte and not byte.