Java8 Programming Examples

Simple way to find if two different lists in Java

java8

import java.util.Arrays;
import java.util.List;
public class Demo {
	public static void main(String[] a) {
		List<Integer>arrList1 = Arrays.asList(new Integer[] { 10, 20, 30, 45, 55, 70, 90, 100 });
		List<Integer>arrList2 = Arrays.asList(new Integer[] {15, 25, 35, 50, 55, 75, 95, 120});
		List<Integer>arrList3 = Arrays.asList(new Integer[] { 10, 20, 30, 45, 55, 70, 90, 100});
		System.out.println("Are List 1 and List2 equal? "+arrList1.equals(arrList2));
		System.out.println("Are List 2 and List3 equal? "+arrList2.equals(arrList2));
		System.out.println("Are List 1 and List3 equal? "+arrList1.equals(arrList3));
	}
}

Check the frequency of an element in Java

java8

import java.util.Arrays;
import java.util.Collections;
import java.util.List;
public class Demo {
	public static void main(String[] args) {
		List<String>list = Arrays.asList("P","Q","R","P","T","P","U","V","W","X","W" );
		int checkOccurrence = Collections.frequency(list, "P");
		System.out.println("Occurrence of P = " + checkOccurrence);
		checkOccurrence = Collections.frequency(list, "W");
		System.out.println("Occurrence of W = " + checkOccurrence);
		checkOccurrence = Collections.frequency(list, "T");
		System.out.println("Occurrence of T = " + checkOccurrence);
	}
}

Check capacity in Java

java8

import java.util.ArrayList;
public class Demo {
	public static void main(String[] a) {
		ArrayList<Integer>arrList = new ArrayList<Integer>(5);
		arrList.add(100);
		arrList.add(200);
		arrList.add(300);
		arrList.add(400);
		arrList.add(500);
		arrList.add(600);
		arrList.add(700);
		System.out.println("Size of list = "+arrList.size());
		arrList.ensureCapacity(15);
		for (Integer number: arrList) {
			System.out.println(number);
		}
		arrList.add(100);
		arrList.add(200);
		arrList.add(300);
		arrList.add(400);
		arrList.add(500);
		System.out.println("Updated list...");
		System.out.println("Size of list = "+arrList.size());
		arrList.ensureCapacity(15);
		for (Integer number: arrList) {
			System.out.println(number);
		}
	}
}

Java Program to convert java.util.Date to ZonedDateTime

java8

import java.time.ZoneId;
import java.time.ZonedDateTime;
import java.util.Date;
public class Demo {
	public static void main(String[] args) {
		Date date = new Date();
		final ZoneId id = ZoneId.systemDefault();
		System.out.println(ZonedDateTime.ofInstant(date.toInstant(), id));
	}
}

Checksum of a Byte Array in Java

java8

import java.util.zip.Adler32;
import java.util.zip.Checksum;
public class Demo {
	public static void main(String[] argv) throws Exception {
		byte[] arr = "This is it!".getBytes();
		Checksum checksum = new Adler32();
		checksum.update(arr, 0, arr.length);
		long res = checksum.getValue();
		System.out.println("Checksum of a Byte array = "+res);
	}
}

Extract multiple integers from a String in Java

java8

import java.util.ArrayList;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class Demo {
	public static void main(String[] args) {
		String str = "(29, 12; 29, ) (45, 67; 78, 80)";
		Matcher matcher = Pattern.compile("\\d+").matcher(str);
		List<Integer>list = new ArrayList<Integer>();
		while(matcher.find()) {
			list.add(Integer.parseInt(matcher.group()));
		}
		System.out.println("Integers = "+list);
	}
}

Java Program to get frequency of words with Lambda Expression

java8

import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
public class Demo {
	public static void main(String[] args) {
		List<String> list = Arrays.asList("Welcome", "to","the","club", "club", "the");
		Map<String, Integer> map = list
		.parallelStream()
		.flatMap(a -> Arrays.asList(a.split(" ")).stream())
		.collect(
		Collectors.toConcurrentMap(c ->c.toLowerCase(), c -> 1,
		Integer::sum));
		System.out.println("Word Frequency = "+map);
	}
}

Display numbers in scientific notation in Java

java8

import java.text.DecimalFormat;
import java.text.NumberFormat;
public class Demo {
	public static void main(String args[]) {
		NumberFormat numFormat = new DecimalFormat();
		int i = Integer.MIN_VALUE;
		System.out.println(i);
		numFormat = new DecimalFormat("0.######E0");
		System.out.println(numFormat.format(i));
		numFormat = new DecimalFormat("0.#####E0");
		System.out.println(numFormat.format(i));
		double val = 0.37872;
		numFormat = new DecimalFormat("0.#####E0");
		System.out.println(numFormat.format(val));
		numFormat = new DecimalFormat("000000E0");
		System.out.println(numFormat.format(val));
	}
}

Set Date value in Java HashMap

java8

import java.util.Calendar;
import java.util.Date;
import java.util.LinkedHashMap;
public class Demo {
	public static void main(String[] argv) {
		Calendar cal = Calendar.getInstance();
		Date date = new Date();
		System.out.println("Date = "+date);
		cal.setTime(date);
		LinkedHashMap<String, Integer>hashMap = new LinkedHashMap<String, Integer>();
		hashMap.put("year", cal.get(Calendar.YEAR));
		hashMap.put("month", cal.get(Calendar.MONTH));
		hashMap.put("day", cal.get(Calendar.DAY_OF_MONTH));
		System.out.println("HashMap (Date) = "+hashMap);
		hashMap.put("hour", cal.get(Calendar.HOUR_OF_DAY));
		hashMap.put("minute", cal.get(Calendar.MINUTE));
		hashMap.put("second", cal.get(Calendar.SECOND));
		hashMap.put("millisecond", cal.get(Calendar.MILLISECOND));
		System.out.println("HashMap (DateTime) = "+hashMap);
	}
}

Display random numbers less than 20 in Java

java8

import java.util.Arrays;
import java.util.Random;
public class Demo {
	public static void main(String[] args) {
		Random rand = new Random();
		int num;
		int arr[] = new int[10];
		for (int j = 0; j<= 9; j++) {
			num = 1 + rand.nextInt(20);
			arr[j] = num;
		}
		System.out.println("Random numbers less than 20 = "+Arrays.toString(arr));
	}
}

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