some question about java OOP

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Java

OOP

Now i have some classes as below:

public class A {
	private static A a = new A();
	private int num1 = 0;
	private int num2 = 0;
	public int getNum1() {
		return num1;
	}
	public void setNum1(int num1) {
		this.num1 = num1;
	}
	public int getNum2() {
		return num2;
	}
	public void setNum2(int num2) {
		this.num2 = num2;
	}
	private  A(){}
	public static A getInstance(){
		return a;
	}
}
public class B {
	private A a = A.getInstance();
	public void setNum1(){
                //some codes was executed and get the result
		a.setNum1(result);
	}
	public void setNum2(){
               //some codes was executed and get the result
		a.setNum2(result);
	}
	public A getA() {
		return a;
	}
	public void setA(A a) {
		this.a = a;
	}
}
public class C {
	public static void main(String[] args) {
		B b = new B();
		A a = b.getA();
		b.setNum1();		//line 1
		b.setNum2();		//line 2
		int num1 = a.getNum1();//line 3
		int num2 = a.getNum2();//line 4
		System.out.println(num1);
		System.out.println(num2);
	}
}

I just want use object a to get the values in class C,why I must use line 1 and 2?
How do i design when delete line 1 and 2 that i also can get the truly values?