Java Packages

// File: com/example/utils/MathUtils.java
package com.example.utils;   // package declaration — must be first line

public class MathUtils {
    public static int square(int n) { return n * n; }
    public static double circleArea(double r) { return Math.PI * r * r; }
}

package com.example;

// Import a specific class
import com.example.utils.MathUtils;

// Import all classes in a package (wildcard)
import java.util.*;

// Static import — import static members directly
import static java.lang.Math.PI;
import static java.lang.Math.sqrt;

public class Main {
    public static void main(String[] args) {
        // Using imported class
        System.out.println(MathUtils.square(5));          // 25
        System.out.println(MathUtils.circleArea(3.0));    // 28.27...

        // Using java.util classes
        List<String> names = new ArrayList<>();
        names.add("Alice");
        names.add("Bob");
        System.out.println(names);  // [Alice, Bob]

        // Using static import — no Math. prefix needed
        System.out.println(PI);          // 3.141592653589793
        System.out.println(sqrt(16.0));  // 4.0
    }
}