Generics

Lesson 33

Generics let code work with multiple data types safely. One method handles integers, strings, objects and more.

Java Track

Save progress as you learn.

61 lessons

Lesson content

Generics allow reusable code across different data types with compile-time safety.

Key Terms

Generics: Work with different types while maintaining safety.
Type Parameter: Placeholder representing a data type.
Compile-Time Safety: Errors caught before runtime.
Generic Method: Uses type parameters for multiple types.

Generic Method Syntax

public <T> void methodName(T parameter) {
    // method body
}

Example: Generic Method to Print Arrays

package com.Genric;

public class GenericMethods {

    public <T> void printArray(T[] array) {
        for (T element : array) {
            System.out.print(element + " ");
        }
        System.out.println();
    }

    public static void main(String[] args) {
        Integer[] intArray = {1, 2, 3, 4, 5};
        String[] stringArray = {"one", "two", "three", "four", "five"};

        GenericMethods genericMethods = new GenericMethods();
        genericMethods.printArray(intArray);
        genericMethods.printArray(stringArray);
    }
}

Output

1 2 3 4 5
one two three four five

Common Type Parameter Names

T — Type
E — Element
K — Key
V — Value
N — Number

Real-World Uses

// Collections
List<String> names;
ArrayList<Integer> numbers;
HashMap<String, Integer> marks;

// Generic class
class Box<T> {
    T value;
}

// Generic interface
interface Data<T> {
    void display(T value);
}

FAQ

1. What are Generics?

Feature allowing classes and methods to work with multiple types safely.

2. What does <T> mean?

Placeholder for a data type. Replaced at compile time.

3. Why use Generics?

Type safety, less code, early error detection.

Generics enable reusable, type-safe code.

<T> is a placeholder for any data type.

One method handles multiple data types.

Errors caught at compile time, not runtime.

Collections use generics heavily.

Avoid raw types. Always specify type.

T, E, K, V are standard naming conventions.

Where Java is used

Java in real-world development

Type Parameter <T>

Placeholder replaced at compile time. Works with any data type.

Generic Method

Declare <T> before return type. Method handles multiple types.

Type Safety

Compiler checks types early. Fewer runtime errors.

Collections

List<String>, ArrayList<Integer>, HashMap<K,V> all use generics.

Generic Class

class Box<T> { T value; } Works with any wrapped type.

Best Practice

Use List<String> not raw List. Always specify the type argument.

Prev: Enumeration (Enum)Back to hub