Summary - Classes

Write a bank account model with classes.

Summary - Classes

A BankAccount class combines owner and balance instance fields, a static totalAccounts counter, a constructor, and a deposit method. The counter increases with each new account.

class BankAccount {
  owner: string;
  balance: number;
  static totalAccounts: number = 0;
  constructor(owner: string) {
    this.owner = owner;
    this.balance = 0;
    BankAccount.totalAccounts++;
  }
  deposit(amount: number): void {
    this.balance += amount;
  }
}

Exercise Write a bank account class

Define a BankAccount class: owner: string and balance: number fields, static totalAccounts: number = 0 counter. The constructor(owner: string) sets balance to 0 and increments BankAccount.totalAccounts. A deposit(amount: number): void method adds to balance. Create two accounts, deposit 100 into one, and print balance and totalAccounts.

Show example solution

class BankAccount {
  owner: string;
  balance: number;
  static totalAccounts: number = 0;
  constructor(owner: string) {
    this.owner = owner;
    this.balance = 0;
    BankAccount.totalAccounts++;
  }
  deposit(amount: number): void {
    this.balance += amount;
  }
}

const a1 = new BankAccount("Ada");
const a2 = new BankAccount("Bob");
a1.deposit(100);
console.log(a1.balance);
console.log(BankAccount.totalAccounts);

Test yourself

What type should the balance field be in a BankAccount class?
- string
- boolean
- static
- number
Show answer

number — Balance is a numeric value, so it should be of type number. static is not a type but an access modifier; string and boolean are wrong types.

Complete the balance initial value

constructor(owner: string) {
    this.owner = owner;
    this.balance = ____;
  }

Show answer

constructor(owner: string) {
    this.owner = owner;
    this.balance = 0;
  }

Bank account parts

class BankAccount

Class definition
constructor(owner: string)

Constructor method
deposit(amount: number)

Instance method
static totalAccounts

Class-level counter

Next lesson: public

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