8. Libraries

8.1. Math

for (int i = 0; i < 5; i++) {
  var num = Math.random();
  var s = String.format("%.5f", num);
  System.out.println(s);
}

8.2. StringBuilder

var entity = "One-Off Coder";
var address = "7526 Old Linton Hall Road";
var city = "Gainesville";
var state = "VA";
var zip = 20155;
var www = "https://www.oneoffcoder.com";
var email = "info@oneoffcoder.com";

var label = new StringBuilder()
    .append(entity).append('\n')
    .append(address).append('\n')
    .append(city).append(' ')
    .append(state).append(' ')
    .append(zip).append('\n')
    .append(www).append('\n')
    .append(email)
    .toString();

System.out.println(label);

8.3. HTTP

import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;

String uri = "http://www.oneoffcoder.com";

HttpClient client = HttpClient.newHttpClient();
HttpRequest request = HttpRequest.newBuilder()
    .uri(URI.create(uri))
    .build();

HttpResponse<String> response =
    client.send(request, HttpResponse.BodyHandlers.ofString());

String body = response.body();

System.out.println(body.length());

8.4. CSV

8.4.1. Writing data to a CSV

import com.opencsv.CSVWriterBuilder;
import com.opencsv.ICSVParser;
import com.opencsv.ICSVWriter;
import java.io.FileWriter;

var writer = new CSVWriterBuilder(new FileWriter("demo.csv"))
    .withSeparator(ICSVParser.DEFAULT_SEPARATOR)
    .withQuoteChar(ICSVParser.DEFAULT_QUOTE_CHARACTER)
    .withEscapeChar(ICSVParser.DEFAULT_ESCAPE_CHARACTER)
    .withLineEnd(ICSVWriter.DEFAULT_LINE_END)
    .build();

var entries = new String[][] {
    { "first_name", "last_name" },
    { "John", "Doe" },
    { "Jane", "Smith" }
};

for (String[] row : entries) {
  writer.writeNext(row);
}

writer.close();

8.4.2. Reading data from a CSV

import com.opencsv.CSVParserBuilder;
import com.opencsv.CSVReaderBuilder;
import com.opencsv.ICSVParser;
import java.io.FileReader;

final var parser = new CSVParserBuilder()
    .withSeparator(ICSVParser.DEFAULT_SEPARATOR)
    .withQuoteChar(ICSVParser.DEFAULT_QUOTE_CHARACTER)
    .withEscapeChar(ICSVParser.DEFAULT_ESCAPE_CHARACTER)
    .build();

final var reader = new CSVReaderBuilder(new FileReader("demo.csv"))
    .withSkipLines(1)
    .withCSVParser(parser)
    .build();

String[] line;
while ((line = reader.readNext()) != null) {
  for (int i = 0; i < line.length; i++) {
    System.out.print(line[i]);
    if (i < line.length - 1) {
      System.out.print(", ");
    } else if (i == line.length - 1) {
      System.out.println();
    }
  }
}

reader.close();

8.5. Static imports

import static java.lang.Math.pow;
import static java.lang.Math.sqrt;

var num = 100.0d;
var s = sqrt(num);
var p = pow(num, 2.0d);

8.6. String tokenization

import java.util.StringTokenizer;

String s = "firstName=John; lastName=John; age=18";

StringTokenizer tokenizer = new StringTokenizer(s, "=;");

while (tokenizer.hasMoreTokens()) {
  String key = tokenizer.nextToken().strip();
  String val = tokenizer.nextToken().strip();

  System.out.println(key + " is " + val);
}

8.7. Optional

8.7.1. Basic use of optional

import java.util.Optional;

var x = Optional.of("John");
// check if empty
System.out.println(x.isEmpty()); // false

// get value
System.out.println(x.get()); // John

8.7.2. Nullable optional

import java.util.Optional;

var x = Optional.ofNullable(null);
// check if empty and presentOptionalExample
System.out.println(x.isEmpty()); // true
System.out.println(x.isPresent()); // false

System.out.println(x.orElse("No name!"));

8.8. Date

8.8.1. Basic date

import java.util.Date;

Date date = new Date();

System.out.println(date.getTime());

8.8.2. Basic calendar

import java.text.SimpleDateFormat;
import java.util.Calendar;
import static java.lang.String.valueOf;
import static java.lang.String.format;

Calendar calendar = Calendar.getInstance();

var month = calendar.get(Calendar.MONTH) + 1;
var day = calendar.get(Calendar.DATE);
var year = calendar.get(Calendar.YEAR);
var hour = calendar.get(Calendar.HOUR);
var minute = calendar.get(Calendar.MINUTE);
var second = calendar.get(Calendar.SECOND);

String date = String.join("-",
    valueOf(year),
    format("%02d", month),
    format("%02d", day));

String time = String.join(":",
    format("%02d", hour),
    format("%02d", minute),
    format("%02d", second));

System.out.println(date + " " + time);

// or use SimpleDateFormat
SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
System.out.println(formatter.format(calendar.getTime()));

8.8.3. Calendar creation

import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.GregorianCalendar;

Calendar calendar = new GregorianCalendar(2019, 0, 31);

SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
System.out.println(formatter.format(calendar.getTime()));

8.8.4. Calendar manipulation

import java.text.SimpleDateFormat;
import java.util.Calendar;

SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");

Calendar calendar = Calendar.getInstance();

// add 1 year
calendar.add(Calendar.YEAR, 1);
System.out.println(formatter.format(calendar.getTime()));

// subtract 2 years
calendar.add(Calendar.YEAR,-2);
System.out.println(formatter.format(calendar.getTime()));

8.9. Random number generation

import java.util.Random;

Random random = new Random(37L);

var a = random.nextBoolean();
var b = random.nextDouble();
var c = random.nextInt();
var d = random.nextInt(100);
var e = random.nextFloat();
var f = random.nextGaussian();
var g = random.nextLong();