Simple Bank Account Program

Hi,

I have a simple program for testing threads below for the standard bank account problem. Can someone explain why I'm getting the following output? I thought that having a synchronized keyword would ensure that the thread would complete the entire method. Thanks.
Jack, Previous balance: 33.0, New balance: 34.0
Jack, Previous balance: 34.0, Jill, Previous balance: 0.0, New balance: 36.0
Jill, Previous balance: 36.0, New balance: 37.0

Code Java:

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public class BankAccountThread extends Thread {
 
	/* Shared variable that is accessed by multiple threads */
	private static double accountBalance;
 
	public BankAccountThread(String name) {
		super(name); 
	}	
 
	public synchronized void deposit(double amount) {
		System.out.print(this.getName() + ", Previous balance: " + accountBalance + ", ");
		accountBalance = accountBalance + amount; 
		System.out.print("New balance: " + accountBalance + "\n");
	}
 
	public void run() {
		for (int i=0; i < 100; i++) {
			deposit(1);
		}
	}	
 
	public static void main(String[] args) {
		new BankAccountThread("Jack").start(); 
		new BankAccountThread("Jill").start();
	}
}

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I recommend reading about Synchronized methods
Synchronized Methods (The Java™ Tutorials > Essential Classes > Concurrency)
In particular the two bullet points about half way down the page, paying special attention to the key phrase 'same object'.