Synchronized methods trouble

Question

hey guys,
I was under the impression that when u use synchronized methods, when a thread calls it any other threads calling it have to wait. If thats true then can someone help me and point out why my threads aren't waiting :(.
import java.util.*;
public class cannibal implements Runnable {
    private static int nonCannibal = 0;
    cannibal(){}
    public synchronized void eat(){
        boolean flag = false;
        try{
            while(nonCannibal == 0){
                if(flag == false){
                    System.out.println("A cannibal waits in the darkness...");
                    flag = true;
                wait();
        }catch(InterruptedException e){
            System.out.println("Some Exception!");
        nonCannibal--;
        System.out.println("Cannibal just ate someone in the woods!");
        System.out.println(nonCannibal +" survivors left!");
    public synchronized void dontEatMe(){
        nonCannibal++;
        notify();
        System.out.println("Unsuspecting person ventures to far out in the woods!");
    public synchronized void run(){
        Random generator = new Random();
        int x = generator.nextInt(2);
        if(x == 0){
            //System.out.println("Cannibal was just summoned!");
            eat();
        }else if(x == 1){
           // System.out.println("Unsuspecting Person just summoned!");
            dontEatMe();
     public static void main(String[] args) {
        Thread []x = new Thread[10];
        for(int i = 0; i < 10; i++){
            x[i] = new Thread(new cannibal());
            x.start();
try{
Thread.currentThread().sleep(3000);
}catch(InterruptedException e){

Answer 1

Demo:
import java.util.Random;
class Account {
    private int balance;
    public synchronized void deposit(int amount) {
        if (amount < 0) throw new IllegalArgumentException();
        System.out.println("increasing balance " + balance + " by " + amount);
        balance += amount;
        notifyAll();
    public synchronized void withdraw(int amount) throws InterruptedException {
        if (amount < 0) throw new IllegalArgumentException();
        while (balance < amount) {
            wait();
        System.out.println("decreasing balance " + balance + " by " + amount);
        balance -= amount;
class Depositer implements Runnable {
    private Account account;
    public Depositer(Account account) {
        this.account = account;
    public void run() {
        try {
            Random rnd = new Random();
            for(int i=0; i<10; ++i) {
                account.deposit(rnd.nextInt(100));
                Thread.sleep(1000);
        } catch(InterruptedException e) {
            e.printStackTrace();
class Withdrawer implements Runnable {
    private Account account;
    public Withdrawer(Account account) {
        this.account = account;
    public void run() {
        try {
            Random rnd = new Random();
            for(int i=0; i<10; ++i) {
                account.withdraw(rnd.nextInt(200));
        } catch(InterruptedException e) {
            e.printStackTrace();
class MainClass {
    public static void main(String[] args) {
        Account acct = new Account();
        Withdrawer out = new Withdrawer(acct);
        Depositer in = new Depositer(acct);
        new Thread(out).start();
        new Thread(in).start();
}