同步线程2

class DataObject {
	int dataItem1;
	int dataItem2;
	DataObject() {
		dataItem1 = 50;
		dataItem2 = 50;
	}
	synchronized void itemSwap() {
		int x = ( int )( -4.999999 + Math.random() * 10 );
		dataItem1 -= x;
		keepBusy( 10 );
		dataItem2 += x; 
	}
	synchronized void test() {
		int sum = dataItem1 + dataItem2;
		System.out.println( sum );
	}
	public void keepBusy( int howLong ) {
		long curt = System.currentTimeMillis();
		while( System.currentTimeMillis() < curt + howLong);
	}
}

class RepeatedSwaps extends Thread {
	DataObject dobj;
	RepeatedSwaps( DataObject d ) {
		dobj = d;
		start();
	}
	public void run() {
		int i = 0;
		while( i++ < 200 ) {
			dobj.itemSwap();
			if( i % 40 == 0 ) {
				dobj.test();
			}
			try {
				sleep( i );
			}catch( InterruptedException e) {}
		}
	}
}

public class SynchedSwaps {
	public static void main(String[] args) {
		DataObject d = new DataObject();
		new RepeatedSwaps( d );
		new RepeatedSwaps( d );
		new RepeatedSwaps( d );
		new RepeatedSwaps( d );
	}	
}