Classes and Objects

Instance Methods

An instance method works with the fields of one object.

instance method An instance method is called on an object and can use that object's state.

Instance Methods

deposit
InstanceMethods.cs
Replay: real traced execution (multi-file project)
using System;

class BankAccount
{
    public int Balance;

    public BankAccount(int balance)
    {
        Balance = balance;
    }

    public void Deposit(int amount)
    {
        Balance += amount;
    }
}

class Program
{
    static void Main()
    {
        int deposit = 5;
        BankAccount account = new BankAccount(10);
        account.Deposit(deposit);

        Console.WriteLine($"deposit={deposit}");
        Console.WriteLine($"balance={account.Balance}");
    }
}

using System;

class BankAccount
{
    public int Balance;

    public BankAccount(int balance)
    {
        Balance = balance;
    }

    public void Deposit(int amount)
    {
        Balance += amount;
    }
}

class Program
{
    static void Main()
    {
        int deposit = 0;
        BankAccount account = new BankAccount(10);
        account.Deposit(deposit);

        Console.WriteLine($"deposit={deposit}");
        Console.WriteLine($"balance={account.Balance}");
    }
}

using System;

class BankAccount
{
    public int Balance;

    public BankAccount(int balance)
    {
        Balance = balance;
    }

    public void Deposit(int amount)
    {
        Balance += amount;
    }
}

class Program
{
    static void Main()
    {
        int deposit = 12;
        BankAccount account = new BankAccount(10);
        account.Deposit(deposit);

        Console.WriteLine($"deposit={deposit}");
        Console.WriteLine($"balance={account.Balance}");
    }
}

  1. deposit ← 5

    19{20    static void Main()21    {22        int deposit→ 5 = 5; //@deposit=0, 1223        BankAccount account = new BankAccount(10);24        account.Deposit(deposit);

  2. public BankAccount(int balance)

    7public BankAccount(int balance10)8{9    Balance = balance10;10}

  3. account ← BankAccount

    22int deposit = 5; //@deposit=0, 1223BankAccount account→ BankAccount = new BankAccount(10);24accountBankAccount.Deposit(deposit5);

  4. public void Deposit(int amount)

    12public void Deposit(int amount5)13{14    Balance += amount5;15}

  5. account.Deposit(deposit);

    23    BankAccount account = new BankAccount(10);24    accountBankAccount.Deposit(deposit5);2526    Console.WriteLine($"deposit={deposit5}");27    Console.WriteLine($"balance={account.Balance15}");28}
    outputdeposit=5
balance=15

  1. deposit ← 0

    19{20    static void Main()21    {22        int deposit→ 0 = 0;23        BankAccount account = new BankAccount(10);24        account.Deposit(deposit);

  2. public BankAccount(int balance)

    7public BankAccount(int balance10)8{9    Balance = balance10;10}

  3. account ← BankAccount

    22int deposit = 0;23BankAccount account→ BankAccount = new BankAccount(10);24accountBankAccount.Deposit(deposit0);

  4. public void Deposit(int amount)

    12public void Deposit(int amount0)13{14    Balance += amount0;15}

  5. account.Deposit(deposit);

    23    BankAccount account = new BankAccount(10);24    accountBankAccount.Deposit(deposit0);2526    Console.WriteLine($"deposit={deposit0}");27    Console.WriteLine($"balance={account.Balance10}");28}
    outputdeposit=0
balance=10

  1. deposit ← 12

    19{20    static void Main()21    {22        int deposit→ 12 = 12;23        BankAccount account = new BankAccount(10);24        account.Deposit(deposit);

  2. public BankAccount(int balance)

    7public BankAccount(int balance10)8{9    Balance = balance10;10}

  3. account ← BankAccount

    22int deposit = 12;23BankAccount account→ BankAccount = new BankAccount(10);24accountBankAccount.Deposit(deposit12);

  4. public void Deposit(int amount)

    12public void Deposit(int amount12)13{14    Balance += amount12;15}

  5. account.Deposit(deposit);

    23    BankAccount account = new BankAccount(10);24    accountBankAccount.Deposit(deposit12);2526    Console.WriteLine($"deposit={deposit12}");27    Console.WriteLine($"balance={account.Balance22}");28}
    outputdeposit=12
balance=22

Follow the Method

  1. deposit starts as 5.
  2. new BankAccount(10) creates an account with balance 10.
  3. account.Deposit(deposit) calls the method on that account.
  4. The method adds 5 to the account balance.
  5. The program prints deposit=5 and balance=15. | starting balance | deposit | final balance | | --- | --- | --- | | 10 | 5 | 15 | | 10 | 0 | 10 | | 10 | 12 | 22 |

Exercise: InstanceMethods.cs

Reproduce deposit=5 and balance=15, then use the pinned deposit variants 0 and 12 to predict balance=10 and balance=22.