Lesson 1: Introduction to Java Standard Library

Overview:

In Lesson 1, we introduce the Java Standard Library, also known as the Java API (Application Programming Interface). The Java API provides a rich set of classes and packages that form the foundation for Java development. This lesson focuses on exploring commonly used packages, such as java.lang and java.util, and understanding their significance in Java programming.

Key Concepts:

  1. Java API (Application Programming Interface):
    • Definition: The Java API is a collection of classes and packages provided by Java for software development.
    • Purpose: It offers a standardized way for Java developers to interact with the core functionality of the Java platform.
  2. java.lang Package:
    • Description: The java.lang package is automatically imported into every Java program. It contains fundamental classes that are essential for basic Java programming.
    • Key Classes:
      • Object: The root class for all Java classes.
      • String: Represents a sequence of characters.
      • System: Provides access to the standard input, output, and error streams.
  3. java.util Package:
    • Description: The java.util package contains utility classes and data structures that are commonly used in Java programs.
    • Key Classes:
      • ArrayList: A dynamic array that can grow or shrink in size.
      • HashMap: An implementation of a hash table for key-value pairs.
      • Scanner: Used for reading input from various sources.

Example:

Let’s explore the java.lang and java.util packages through a simple program. We’ll use the String class from java.lang and the ArrayList class from java.util.

import java.util.ArrayList;

public class JavaAPIDemo {

    public static void main(String[] args) {
        // Example from java.lang package
        String greeting = "Hello, Java!";
        System.out.println(greeting);

        // Example from java.util package
        ArrayList<String> fruits = new ArrayList<>();
        fruits.add("Apple");
        fruits.add("Banana");
        fruits.add("Orange");

        System.out.println("Fruits: " + fruits);
    }
}

In this example, we use the String class from java.lang to work with a text string and the ArrayList class from java.util to create and manipulate a dynamic list of fruits. This demonstrates how fundamental classes from these packages are used in a typical Java program.