simple example of using 'synchronized'

gistfile1.java

public class Main {

    public static void main(String[] args) {

        String[] words = {"a", "b", "c", "a", "a", "r", "b", "c", "a"};

        SharedValue sharedValue = new SharedValue();

        for (int i = 0; i <= 6; i += 3) {
            Thread t = new Thread(new Worker(words,i,i+2,"a",sharedValue));
            t.start();
            try { t.join(); } catch (InterruptedException e) {}
            // we use t.join() to make sure that all threads complete before
            // printing the result
        }
        System.out.println(sharedValue.getContents());
        System.exit(0);
    }
}



class Worker implements Runnable {

    private int i;
    private int j;
    private String[] values;
    private String key;
    private SharedValue sharedValue;

    public Worker(String[] values, int start, int stop, String key, SharedValue sharedValue) {
        this.i = start;
        this.j = stop;
        this.values = values;
        this.key = key;
        this.sharedValue = sharedValue;
    }

    @Override
    public void run() {
        for (; i <= j; i++) {
            if (values[i].equals(key)) {
                System.out.println("match found at index " + i);
                sharedValue.increment();
            }
        }
    }
}


class SharedValue {

    private Integer number = 0;

    public SharedValue() {}

    public Integer getContents() {
        return number;
    }

    public synchronized void increment() {
        number++;
    }

}