public class Couple {
String a;
String b;

public Couple() {
    a=null;
    b=null;
}

public class Couple {
String a;
String b;

public Couple() {
    a=null;
    b=null;
}

public void setA(String v) {
    synchronized(a) {
        while(a!=null)
            try {
                wait();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        a=v;
        this.notifyAll();
    }
}

public void setB(String v) {
    synchronized(b) {
        while(b!=null)
            try {
                wait();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        b=v;
        this.notifyAll();
    }
}

public String getA() {
    synchronized(a) {
        while(a==null)
            try {
                wait();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        String result = a;
        a = null;
        this.notifyAll();
        return result;
    }
}

public String getB() {
    synchronized(b) {
        while(b==null)
            try {
                wait();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        String result = b;
        b = null;
        this.notifyAll();
        return result;
    }
}