Strange Error [java.lang.ArrayIndexOutOfBoundsException]

[Ronald Vermeij]

Hello Java Experts,

1. I have three classes
- Launcher........... (which launches 1 Parallel_Thread thread and 1 Shared Object)
- Parallel_thread.. (which talks twice to the shared object and then terminates)
- SharedObject.....(which runs until it is shut-down by the launcher class)

2. All Classes "javac" without any errors!

3. This is the Launcher Code

public class Launcher {
  public static void main (String args[]){
    
    // declare thread"
    Parallel_thread p1;
    // declare shared object
    SharedObject so1;
    // some constants to play with    
    int Max_Number_of_Threads = 1;
    int DelayInterval_per_Thread = 100;
    
    System.out.println("Launcher - Start");
    
    // create new SharedObject thread and start it
    so1 = new SharedObject(1, 100);
    so1.start();
    
    //create new thread and start it
    p1 = new Parallel_thread(1,1000,so1);
    p1.start();
    
    // wait for started thread to join the Launcher
    try {
    	p1.join();
    } catch (InterruptedException e) {
    } // try
    
    // terminate SharedObject thread  
    so1.shutdown();
    
    // end of scheduler program
    System.out.println("Launcher - Terminated");
  } //main
} // class 

When running the launcher.class via java launcher<enter> from the commandline, this is the error that appears

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0 at Launcher.main(Launcher.java:57)

Now my questions about this message?
1. How is it possible to get an ArrayIndexOutOfBoundsException error?
I do not enter any commandline arguments when starting this class, so the Args[] array is not being used.

2. How is it possible to get an error in LINE 57, while my Launcher.java sourcecode is only 33 lines???
This is really weird to me :~}

Thanks for sharing your insights with me.

Ronald

[fred rosenberger]

is that the full error message?

[Tom Reilly]

A couple of suggestions/questions:

1. When you launch by: java launcher<enter>, I assume you mean java Launcher<enter>. Or could it be that you are not running the code that you think you are?

2. Try putting in more logging to narrow down the statement that causes the error. Does the "Launcher - Start" appear in the output?

3. How are your two threads communicating?

4. You don't show the code for SharedObject and Parallel thread. What do they do?

[Paul Clapham]

The error message you posted was thrown from line 57 of the Launcher class, in the main() method. But the code you posted for the Launcher class doesn't even have 57 lines. So the code you posted isn't the code which threw that exception. Fix that problem first.

[Ronald Vermeij]

The story continues, At first here are all sourcecodes

1. Launcher.java

public class Launcher {
  public static void main (String args[]){
    
    // declare thread"
    Parallel_thread p1;
    SharedObject so1;
    
    int Max_Number_of_Threads = 1;
    int DelayInterval_per_Thread = 100;
    
    System.out.println("Launcher - Start");
    
    // create new SharedObject thread and start it
    so1 = new SharedObject(1, 100);
    so1.start();
    
    //create new thread and start it
    p1 = new Parallel_thread(1,1000,so1);
    p1.start();
    
    // wait for started thread to join the Launcher
    try {
    	p1.join();
    } catch (InterruptedException e) {
    } // try
    
    // terminate SharedObject thread  
    so1.shutdown();
    
    // end of scheduler program
    System.out.println("Launcher - Terminated");
  } //main
} // class 

2. Parallel_thread

public class Parallel_thread extends Thread {
  private int Thread_ID = 0; 
  private int Thread_Sleep_Interval = 0;
  
  // pointer to shared object
  // mutex boolean that tells if the shared object is locked (yes/no)
  private SharedObject SO;
  private boolean HASACCESS = false;
  
  // constructor
  public Parallel_thread(int ID, int Thread_Interval, SharedObject so) {
    Thread_ID = ID;
    this.SO = so;
    Thread_Sleep_Interval = Thread_Interval;
    
    System.out.print("Thread:");
    System.out.print(Thread_ID);
    System.out.println(" - Created");
  }  
    
  public void run(){
    System.out.print("Thread:");
    System.out.print(Thread_ID);
    System.out.println(" - Started");

    SO.deposit(Thread_ID, 1000);	
    
    try {
	Thread.sleep(Thread_Sleep_Interval);
      } catch (InterruptedException e) {
      } // try
    
    SO.withdraw(Thread_ID, 500);
    
    // Introducting thread sleep for other threads
    try {
      Thread.sleep(Thread_Sleep_Interval);
    } catch (InterruptedException e) {
    }
        
    System.out.print("Thread:");
    System.out.print(Thread_ID);
    System.out.println(" - Terminated");    
  } // run
} // class

3. Shared Object

public class SharedObject extends Thread {
  int SharedObject_ID = 0;
  int SharedObject_content = 0;

  int Thread_Sleep_Interval = 0;
  int teller = 0;
  //
  boolean AccessGranted = true;
  boolean stop = false;
            
  // SharedObject Constructor
  public SharedObject(int ID, int Thread_Interval) {
    SharedObject_ID = ID;
    Thread_Sleep_Interval = Thread_Interval;
    System.out.print("SharedObject:");
    System.out.print(SharedObject_ID);
    System.out.println(" - Created");
  }
  
  public SharedObject() {
    SharedObject_ID = 1;
    Thread_Sleep_Interval = 1000;
    System.out.print("SharedObject:");
    System.out.print(SharedObject_ID);
    System.out.println(" - Created");
  }  

  // SharedObject main Thread Loop  
  public void run(){
    // thread loop - startup message
    System.out.print("SharedObject:");
    System.out.print(SharedObject_ID);
    System.out.println(" - Started");
          
    // Thread sleep to allow other thread to run
    // return thread control to thread-scheduler
    while (!stop)
    {
      try {
	Thread.sleep(Thread_Sleep_Interval);
      } catch (InterruptedException e) {
	System.out.print("SharedObject:");
	System.out.print(SharedObject_ID);
	System.out.println(" - Sleeps");
      } // try
    } // while
  } // run

  public synchronized void deposit(int ID, int deposit_amount) {
    SharedObject_content = SharedObject_content + deposit_amount;
    System.out.print("SharedObject - ATM:");
    System.out.print(ID);
    System.out.print(" deposits:");
    System.out.print(deposit_amount);
    System.out.print(" Content:");
    System.out.println(SharedObject_content);
  }
  
  public synchronized void withdraw(int ID, int withdraw_amount) {
    SharedObject_content = SharedObject_content - withdraw_amount;
    System.out.print("SharedObject - ATM:");
    System.out.print(ID);
    System.out.print(" withdraws:");
    System.out.print(withdraw_amount);
    System.out.print(" Content:");
    System.out.println(SharedObject_content);
  }

  public synchronized void shutdown() {
    System.out.print("SharedObject:");
    System.out.print(SharedObject_ID);
    System.out.println(" - Shutting Down");
    stop = true;
  }
} // class

4. Some diagnostic background info:

ronald@camelion:~/Desktop/java_exercisis/threads/a/example0_thread_templates> java -version
java version "1.6.0_20"
Java(TM) SE Runtime Environment (build 1.6.0_20-b02)
Java HotSpot(TM) Client VM (build 16.3-b01, mixed mode)

5. Full error message after:
- removing all previous classfiles in the directory
- recompiling from the command-line with java /absolute/PATH/to/the/.java file

ronald@camelion:~/Desktop/java_exercisis/threads/a/example0_thread_templates> java Launcher
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0
at Launcher.main(Launcher.java:57)
ronald@camelion:~/Desktop/java_exercisis/threads/a/example0_thread_templates>

I am wondering if you get the same results (error), when compiling these source-codes?

[Ulf Dittmer]

I concur with Paul's post: you're not running the code that you think you're running. When I compile and run the code I get this output:

Launcher - Start
SharedObject:1 - Created
SharedObject:1 - Started
Thread:1 - Created
Thread:1 - Started
SharedObject - ATM:1 deposits:1000 Content:1000
SharedObject - ATM:1 withdraws:500 Content:500
Thread:1 - Terminated
SharedObject:1 - Shutting Down
Launcher - Terminated

[Lalit Mehra]

i agree with Ulf ... even i ran it and it is running just fine

[Rob Spoor]

Perhaps you are using older versions of your class files. Try throwing your class files away, then recompiling your source code.

[Ronald Vermeij]

Ulf Dittmer wrote:I concur with Paul's post: you're not running the code that you think you're running. When I compile and run the code I get this output:

Launcher - Start
SharedObject:1 - Created
SharedObject:1 - Started
Thread:1 - Created
Thread:1 - Started
SharedObject - ATM:1 deposits:1000 Content:1000
SharedObject - ATM:1 withdraws:500 Content:500
Thread:1 - Terminated
SharedObject:1 - Shutting Down
Launcher - Terminated

THAT is the result i was searching for too Ulf! Thanks for the feedback and from running it on your own system.


UPDATE for all
1. I have searched my entire harddisk(s) and found NO second copy of Launcher.java and Launcher.class (not even in hidden directories, "recycle bin" or "Trash/files" directories.

2. I have removed all .class files from the working directory and recompiled the 3 sourcecodes again -> Same error!

3. Finally i found a "solution:"
- I renamed - the Launcher class to Ronald class (in line 1 of the Launcher.java file)
- I renamed - the file Launcher.java to Ronald.java
- I recompiled this Ronald.java example ..... en voila... error gone :-) so this problem is solved

4. It still keeps wondering/bugging me how it was possible that this error occurred? An error inline 57 of a 34 line sourecode.

Questions
A - Is it possible that there is was another Launcher.java, Lancher.class file on my system -> No rule out that one by a disk search.
B - Does the JAVAC compiler itself store any old compilation results (class files) for possible re-use? or faster re-compilation
C - When I enter Javac <filename.java> HOW does JAVAC find the filename.java:
----- Does JAVAC search in the current directory first?
----- Does JAVAC search along the PATH of the computer it runs on?
----- Option 3?

Thank you all for your valuable feedback and explanation on this "error".

[Vijitha Kumara]

Ronald Vermeij wrote:B - Does the JAVAC compiler itself store any old compilation results (class files) for possible re-use? or faster re-compilation

Only the last compiled one unless you moved it after the compilation or use -d with "javac" to compile it to another location.

C - When I enter Javac <filename.java> HOW does JAVAC find the filename.java:

If it's only the file name then it assumes it is from the current directory, or in the full path to the source file if given.

Does JAVAC search along the PATH of the computer it runs on?

PATH is for a different purpose, to make the executable files available to the command prompt.

[Ronald Vermeij]

@Rob: Look to previous ans first reply..
Before re-compiling, I have (always) removed all old class file in same folder each time.

@Vijitha: Thanks for your answers on the Javac compiler.

[Tom Reilly]

Perhaps the Launcher.class file is in a jar file in your classpath.