Substitutepublic class Substitute extends Object | This example shows how to use the readResolve method.
This method resolves the object
read from the stream before it is returned to the caller.
The writeReplacea method allows an object to nominate its
own replacement in the stream before the object is written.
This example creates a symbol class for which only a single instance of
each symbol binding exists. The Symbol class defines the
readResolve method. A symbol is created from outside using the
symbollookup method, which finds and returns a symbol if one already
exists and creates one, if one does not. This assures uniqueness within
one VM. Then, when readResolve is called when the symbol is being read,
a preexisting equivalent Symbol object is substituted from the hashtable
to maintain the unique identity constraint, if such a symbol exists.
Otherwise, the new symbol is added to the hashtable and returned. This
assures uniqueness when we are dealing with more than one VM.
How to Run:
Compile this file: javac Substitute.java
Run this file: java Substitute
This will print out a confirmation that the two symbols that were
serialized separately but had the same name are indeed the same symbol.
Compiled and Tested with JDK1.2 |
| Methods Summary |
|---|
| public static void | main(java.lang.String[] args)Basically, serialize and deserialize two symbols with the same
name and show that they are actually the same symbol.
// create a few symbols to be serialized
Symbol s1 = Symbol.symbolLookup("blue");
Symbol s2 = Symbol.symbolLookup("pink");
Symbol s3 = Symbol.symbolLookup("blue");
// use these to deserialize the symbols
Symbol obj1 = null, obj2 = null, obj3 = null;
// serialize the symbols
try {
FileOutputStream fo = new FileOutputStream("symbol.tmp");
ObjectOutputStream so = new ObjectOutputStream(fo);
so.writeObject(s1);
so.writeObject(s2);
so.writeObject(s3);
so.flush();
} catch (Exception e) {
System.out.println(e);
System.exit(1);
}
// deserialize the symbols
try {
FileInputStream fi = new FileInputStream("symbol.tmp");
ObjectInputStream si = new ObjectInputStream(fi);
obj1 = (Symbol) si.readObject();
obj2 = (Symbol) si.readObject();
obj3 = (Symbol) si.readObject();
} catch (Exception e) {
System.out.println(e);
System.exit(1);
}
// show the uniqueness
if (obj1 == obj3) {
System.out.println("Symbol1 and Symbol3 are the same!");
}
|
|
