Functions

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Functions1.java

public class Functions1 {

	static void printHello() {
		System.out.println("Hello, world!");
	}

	public static void main(String[] args) {
		printHello();
	}
}

Functions2.java

public class Functions2 {

	static void printHello(String name) {
		System.out.println("Hello, " + name + "!");
	}

	public static void main(String[] args) {
		printHello("Fred");
		printHello("Wilma");
		printHello("Barney");
		printHello("Betty");
	}
}

Functions3.java

import org.pureprogrammer.Utils;

public class Functions3 {

	static int squared(int j) {
		return j * j;
	}

	public static void main(String[] args) {
		for (int i = 1; i <= 10; ++i) {
			System.out.println(Utils.format("{0:d}^2 = {1:d}", i, squared(i)));
		}
	}
}

Functions4.java

import org.pureprogrammer.Utils;

public class Functions4 {

	static double exponentiation(double base, int powerArg) {
		int power = powerArg;
		double result = 1;
		while (power > 0) {
			result *= base;
			--power;
		}
		return result;
	}

	public static void main(String[] args) {
		for (double b = 1.1; b < 2.05; b += 0.1) {
			for (int p = 2; p <= 10; ++p) {
				System.out.println(Utils.format("{0:f} ^ {1:d} = {2:f}", b, p, exponentiation(b, p)));
			}
		}
	}
}

Functions5.java

import org.pureprogrammer.Utils;

public class Functions5 {

	static long factorial(int x) {
		if (x <= 1) {
			return 1;
		}
		return x * factorial(x - 1);
	}

	public static void main(String[] args) {
		for (int x = 1; x < 10; ++x) {
			System.out.println(Utils.format("{0:d}! = {1:d}", x, factorial(x)));
		}
	}
}

Lists6.java

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import org.pureprogrammer.Utils;

public class Lists6 {

	static List<String> reverseList(final List<String> x) {
		List<String> y = new ArrayList<>();
		for (int i = x.size() - 1; i >= 0; --i) {
			y.add(x.get(i));
		}
		return y;
	}

	public static void main(String[] args) {
		List<String> names = Utils.listFromStrings(new String[]{"Fred", "Wilma", "Barney", "Betty"});

		for (String name : names) {
			System.out.println("Hello, " + name + "!");
		}

		names = reverseList(names);
		for (String name : names) {
			System.out.println("Hello, " + name + "!");
		}

		System.out.println(Utils.listToString(names));
	}
}

Maps3.java

import java.util.HashMap;
import java.util.Map;
import org.pureprogrammer.Utils;

public class Maps3 {

	static Map<String, Integer> convertKMtoMiles(final Map<String, Integer> x) {
		Map<String, Integer> y = new HashMap<>();
		for (String planet : x.keySet()) {
			y.put(planet, (int)(x.get(planet) * 0.621371 + 0.5));
		}
		return y;
	}

	public static void main(String[] args) {
		Map<String, Integer> planetDiametersInKM = Utils.map(new Object[][] {
			{"Mercury", 4879},
			{"Venus", 12103},
			{"Earth", 12756},
			{"Mars", 6794},
			{"Jupiter", 142985},
			{"Saturn", 120534},
			{"Uranus", 51115},
			{"Neptune", 49534},
			{"Pluto", 2374},
			{"Ceres", 946},
			{"Eris", 2326},
			{"Makemake", 1430}
		});

		Map<String, Integer> planetDiametersInMiles = convertKMtoMiles(planetDiametersInKM);
		for (String planet : planetDiametersInMiles.keySet()) {
			System.out.println(planet + " has a diameter of " + planetDiametersInMiles.get(planet) + " miles");
		}
	}
}

Tuples3.java

import org.pureprogrammer.Tuple;
import org.pureprogrammer.Utils;

public class Tuples3 {

	static Tuple.T2<Integer, String> swap(final Tuple.T2<String, Integer> x) {
		Tuple.T2<Integer, String> y;
		y = Tuple.makeTuple(x.second(), x.first());
		return y;
	}

	public static void main(String[] args) {
		Tuple.T2<String, Integer> pair1 = Tuple.makeTuple("Hello", 5);
		Tuple.T2<Integer, String> pair2;
		pair2 = swap(pair1);
		System.out.println(Utils.tupleToString(pair1) + " becomes " + Utils.tupleToString(pair2));
	}
}

Questions

• {{Who's on first?}}
• {{Who's on second?}}
• {{Who's on third?}}

Projects

More ★'s indicate higher difficulty level.

• Alouette Lyrics
• Bingo Lyrics
• 99 Bottles of Beer Lyrics
• Bubble Sort
• Calculate Euler's Number
• Compute π Function
• Compute π (Monte Carlo with Central Limit Theorem)
• Credit Card Validator
• The Farmer in the Dell (Revisited)
• Fibonacci Numbers
• Football Passer Rating (Revisited)
• GCD
• Insertion Sort
• LCG Pseudo-Random Number Generator
• License Plate Generator (Revisited)
• Merge Sort
• Min/Max Functions
• Old MacDonald Lyrics
• Quicksort
• Renard Numbers with Rounding Function
• Roman Numerals
• Sign Function
• Spreadsheet Columns
• Tower of Hanoi
• Twelve Days of Christmas Lyrics

References

• [[Java Language Specification]], Java SE 17 Edition, Gosling, et. al., 2021.
• [[Java Tutorials]]
• [[Java at TutorialsPoint]]
• Download Java at [[Amazon Corretto]], [[Azul Zulu]], [[Eclipse Temurin]] or [[Oracle JDK]]