인스턴스와 참조변수

package javaFirstClass;

public class BankAccount {
	
	public static void main(String[] args) {
		DupRef ref1 = new DupRef();
		DupRef ref2 = ref1;
		
		ref1.deposit(3000);
		ref2.deposit(2000);
		ref1.withdraw(400);
		ref2.withdraw(300);
		ref1.checkMyBalance();
		ref2.checkMyBalance();
	}

}

class DupRef{
	int balance =0;
	 
	public int deposit(int amount) { //입금
		balance+=amount;
		return balance;
	}
	
	public int withdraw(int amount) { //출금
		balance-=amount;
		return balance;
	}
	
	public int checkMyBalance() { //예금 조회
		System.out.println("잔액: " + balance);
		return balance;
	}
}

잔액: 4300
잔액: 4300