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Java Forum / General / February 2007How to convert an Object reference to an integer?
I need to convert an Object reference to an integer. How to do it? > I need to convert an Object reference to an integer. How to do it? As it is, the question is very unclear. What properties of the object should the resulting integer reflect? F. Berisha Well, Your question is not clear but if i am getting it correctly then you need to override toString() method in your class. public String toString() { // return something that has an integer.. } now if you have something like :- MyClass c = new MyClass then do the following :- Integer.parseInt(c); Is that You wanted?? > > I need to convert an Object reference to an integer. How to do it? > > As it is, the question is very unclear. > What properties of the object should the resulting integer reflect? > > F. Berisha > Well, Your question is not clear but if i am getting it correctly then > you need to override toString() method in your class. [quoted text clipped - 10 lines] > > Is that You wanted?? I don't claim to know what the OP is actually asking for, but if your interpretation is the correct one, I fail to see the logic in returning the integer as a String that needs to be parsed. If you are in control of the object code to begin with, return the value directly, from a suitably named method: public int toSomeNumber() { return someNumber; } /gordon  Signature[ don't email me support questions or followups ] g o r d o n + n e w s @ b a l d e r 1 3 . s e > I need to convert an Object reference to an integer. How to do it? Depends on the object. Consider <http://java.sun.com/javase/6/docs/api/java/lang/Integer.html#parseInt(java.lang. String)> with <http://java.sun.com/javase/6/docs/api/java/lang/Object.html#toString()> Of course, if the object is an Integer it's easier than that. - Lew > I need to convert an Object reference to an integer. How to do it? Sorry. I did not make it clear. I want to convert an Object reference to an integer. And save the integer. When use the object again, I look up the reference by that integer key. Now I know System.identityHashCode(object) can give me an unique integer. >> I need to convert an Object reference to an integer. How to do it? > [quoted text clipped - 3 lines] > integer key. Now I know System.identityHashCode(object) can give me an > unique integer. It MAY give you a unique key. It cannot always guarantee that. In particular, a 64 bit JVM on a large system may have more objects than there are distinct values of int. Why is it better/easier to remember the int than the object reference? Patricia >> I need to convert an Object reference to an integer. How to do it? > > Now I know System.identityHashCode(object) can give me an > unique integer. Read the javadoc more closely. There's no guarantee that the output of System.identityHashCode() is unique. Two separate objects might give the same integer result. If you need guaranteed unique integers, you're out of luck. Here's a quote from the version 1.5 javadoc for Object.hash() which is referenced by System.identityHashCode(). Highlighting is mine. **As much as is reasonably practical**, the hashCode method defined by class Object does return distinct integers for distinct objects. (This is typically implemented by converting the internal address of the object into an integer, but this implementation technique is not required by the JavaTM programming language.) What are you doing that you can store an integer key but you can't store an object reference? If it's to interface with an external system, could you use a string instead? That way you could (in some application-dependent way) define a string that maps uniquely to the object. Use a HashMap with the string as the key and object as the value. Or for that matter, if you can define (in some application-dependent way) an integer that maps uniquely to the object, use that instead of a String. But it would have to be application-dependent based on the properties of the object or other application-specific logic. I don't think you'll find a guaranteed-unique, system-generated integer to map to an object. Regards, John > >> I need to convert an Object reference to an integer. How to do it? > [quoted text clipped - 29 lines] > Regards, > John It is a requirement by JNI. I package object values to a byte buffer. As we know, C++ has address and can convert to an integer. I cannot package Object reference to a byte buffer, so I need convert it to an unique integer. To illustrate it, see below. |-----------------------| | Type | ------------------------ | Length | ------------------------ | Address | ------------------------- JNI takes the third element as an address, i.e. an unique integer, I hope to package the Java object reference. Because the object reference is like an address. But Java does not permit converting a reference to an integer. > It is a requirement by JNI. > I package object values to a byte buffer. As we know, C++ has address [quoted text clipped - 15 lines] > Because the object reference is like an address. But Java does not > permit converting a reference to an integer. Holy cow, you're talking JNI, not just Java. That's a completely different thing! You're not getting much help because you're not asking your question very well. How about starting over. Something like... "I want to use JNI function X() to accomplish Y. I'm having trouble understanding how to format the data for parameter Z." Fill in those blanks and a bit of explanation and you've got a much better chance of getting help. Better still, go to http://www.google.com/codesearch and type in the JNI function you're trying to use. You'll probably come up with 100 examples of code using it. Browse a few examples and you might find one that helps you out. I'm afraid my JNI is rusty enough that I probably won't be any more help. Good luck, John > It is a requirement by JNI. > I package object values to a byte buffer. As we know, C++ has address [quoted text clipped - 15 lines] > Because the object reference is like an address. But Java does not > permit converting a reference to an integer. No but C does. Pass the reference to the JNI function *as a reference* (i.e. a jobject?), then convert it to int or long in there. You also have to do something to lock the address while you're using it but it's nearly ten years since I did this and I can't remember the details. It is a requirement by JNI. I package object values to a byte buffer. As we know, C++ has address and can convert to an integer. I cannot package Object reference to a byte buffer, so I need convert it to an unique integer. To illustrate it, see below. |-----------------------| | Type | ------------------------ | Length | ------------------------ | Address | ------------------------- JNI takes the third element as an address, i.e. an unique integer, I hope to package the Java object reference. Because the object reference is like an address. But Java does not permit converting a reference to an integer. [http://www.javolution.org/api/javolution/io/Struct.html] > I need to convert an Object reference to an integer. How to do it? Hi, You can use the following statement to convert from Object to integer. Integer.parseInt(String.valueOf(object)); Here 'object' must contain integer reference value then only it will works otherwise it throws NumberFormatException. Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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