Java generic boundaries and their role

Java Generic boundaries specify constraints on type parameters, ensuring that only types that satisfy these constraints can be used. There are two types of generic bounds: upper bounds (extends) and lower bounds (super). An upper bound requires that the type parameter be a subclass of the specified type, while a lower bound requires that the type parameter be a superclass of the specified type. Generic boundaries enhance type safety, improve performance, and code readability.

Java Generic Boundaries and Its Role

Overview

Generics is a powerful feature in Java that allows us to create classes and methods that work with different types of data. Generic bounds enable us to specify constraints on type parameters, ensuring that only types that satisfy these constraints can be used.

Generic boundary types

Java provides two types of generic boundaries:

• Upper bound (extends) :The type parameter must be a subclass of the specified type or itself.
• Lower bound (super): The type parameter must be a superclass of the specified type or itself.

Using generic boundaries

When using generic boundaries, we will specify the boundaries in the generic declaration:

<T extends Number> // 上限边界

## The #extends keyword indicates that T must be a subclass of the Number class or Number itself. The

<? super String> // 下限边界

super keyword indicates that T must be a superclass of the String class or String itself.

Practical Case

LinkedList to store numbers and use an upper bound to ensure that the list only contains Number Type:

import java.util.LinkedList;

class NumberList<T extends Number> {
    private LinkedList<T> numbers;

    public NumberList() {
        numbers = new LinkedList<>();
    }

    public void add(T number) {
        numbers.add(number);
    }

    public T get(int index) {
        return numbers.get(index);
    }
}

T is restricted to a subclass of Number, which means we can only add and retrieve Number and its subclasses such as Integer and Double.

Benefits

Enhanced type safety: it helps prevent incorrect types from being Passed to a generic class or method.
• Improved performance: The compiler can perform better optimizations because it knows the constraints of a specific type.
• Improve code readability: Generic boundaries make code easier to understand because they clearly specify the acceptable data types.

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