AP CSA 1.14 Exercise 1: Working the Account

Unit 1: Using Objects and Methods · Lesson 1.14 · Exercise 1

Working the Account

Calling Instance Methods. Write real Java, run it, and submit it to be graded against hidden test cases.

Back to the Lesson 1.14 page All Unit 1 lessons

Why this one is worth doing

Some methods change the object and return nothing. Some return a value and change nothing. Telling them apart from the call alone is what this exercise drills.

What to write

The Account class is written for you. Do not change it.
Read an opening balance, a deposit and a withdrawal, all integers.
Create one Account with the opening balance.
Call deposit, then print the balance.
Call withdraw, then print the balance.
Print the number of transactions the account has recorded.

Your program reads

Three integers on separate lines: opening, deposit, withdrawal.

Your program prints

Three lines: the balance after the deposit, the balance after the withdrawal, and the transaction count.

Worked examples

These are the cases you can see. There are more you cannot, and they use different values, so an answer that prints these numbers as constants will fail.

Example 1 input

100
50
30

Example 1 output

150
120
2

Example 2 input

0
0
0

Example 2 output

0
0
2

Your answer

Main.java

import java.util.Scanner;

class Account {
  private int balance;
  private int transactions;

  public Account(int balance) { this.balance = balance; }

  public void deposit(int amount) { balance += amount; transactions++; }

  public void withdraw(int amount) { balance -= amount; transactions++; }

  public int getBalance() { return balance; }

  public int getTransactions() { return transactions; }
}

public class Main {
  public static void main(String[] args) {
    Scanner input = new Scanner(System.in);
    int opening = input.nextInt();
    int in = input.nextInt();
    int out = input.nextInt();

    // One account, two changes, three printed lines.
  }
}

Input for the Run button

Run sends whatever is in the input box below. Submitting runs your program against every test case, including hidden ones with different input.

Stuck?

Hint 1

deposit returns void, so System.out.println(acct.deposit(in)) will not compile. Call it, then ask for the balance separately.

Hint 2

getBalance returns an int and changes nothing, so calling it twice in a row gives the same answer twice.

Hint 3

The account can go negative. Nothing in the class stops a withdrawal, and this exercise does not ask you to.

Where to go next

Rework the Lesson 1.14 page Pick another Unit 1 lesson

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