Generic classes

Learn type-safe collections with generic classes.

Generic class definition

A generic class takes a type parameter in <T> right after the class name. The parameter can be used in all fields and methods. Each instance fixes the type, so a Kutu<string> only holds strings.

class Kutu<T> {
  private icerik: T;
  constructor(icerik: T) {
    this.icerik = icerik;
  }
  al(): T { return this.icerik; }
}
const k = new Kutu<string>("merhaba");
console.log(k.al());  // merhaba

Type-safe collections

Generic classes are ideal for writing type-safe collections. Stack, queue, tree structures can be written once as a generic class and used with any type. new Depo<number>() creates an instance that stores numbers, new Depo<string>() one that stores strings.

Exercise Type-safe storage

Write a generic class Depo<T>. It should have a private field ogeler: T[] starting as an empty array. Method ekle(o: T): void pushes an item; method al(i: number): T returns the item at the given index. Then create a Depo<string> instance, add "elma", and print the result of al(0).

Show example solution

class Depo<T> {
  private ogeler: T[] = [];
  ekle(o: T): void {
    this.ogeler.push(o);
  }
  al(i: number): T {
    return this.ogeler[i];
  }
}
const d = new Depo<string>();
d.ekle("elma");
console.log(d.al(0));

Test yourself

Where is the type parameter written in a generic class?
- Right after the class name, inside angle brackets
- At file top with a type T declaration
- As a constructor parameter
- After the method name
Show answer

Right after the class name, inside angle brackets — In a generic class the type parameter is written inside angle brackets right after the class name.

Generic class instance

class Kutu<T> {
  private deger: T;
  constructor(deger: T) { this.deger = deger; }
  al(): T { return this.deger; }
}
const k = new Kutu<____>(42);

Show answer

class Kutu<T> {
  private deger: T;
  constructor(deger: T) { this.deger = deger; }
  al(): T { return this.deger; }
}
const k = new Kutu<number>(42);

Generic class parts

class Kutu<T>

Generic class declaration
new Kutu<number>(5)

Generic class instance
private icerik: T

Type parameter as field
al(): T

Type parameter as return type

Next lesson: Multiple type parameters

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