Java8 Programming Examples

Convert Wrapper value array list into primitive array in Java

java8

import java.util.ArrayList;
public class Demo {
	public static void main(String[] args) {
		ArrayList<Integer>arrList = new ArrayList<Integer>();
		arrList.add(5);
		arrList.add(10);
		arrList.add(15);
		arrList.add(20);
		arrList.add(25);
		arrList.add(30);
		arrList.add(45);
		arrList.add(50);
		final double[] arr = new double[arrList.size()];
		int index = 0;
		for (final Integer value: arrList) {
			arr[index++] = value;
		}
		System.out.println("Elements of double array...");
		for (Double i: arr) {
			System.out.println(i);
		}
	}
}

Generate two separate outputs using Random in Java

java8

import java.util.Random;
public class Demo {
	private static final Random r = new Random();
	public static void main(String[] args) {
		int val = 5;
		while (val<= 100) {
			System.out.printf("%-4d", r.nextInt(20) * 1);
			if (val % 5 == 0) {
				System.out.println();
			}
			val++;
		}
		System.out.println();
		val = 20;
		while (val<= 100) {
			System.out.printf("%-4d", r.nextInt(10 * (20)));
			if (val % 5 == 0) {
				System.out.println();
			}
			val++;
		}
	}
}

Generate a random string in Java

java8

import java.util.Random;
public class Demo {
	public static void main(String[] args) {
		String[] strArr = { "P", "Q", "R", "S","T", "U", "V", "W" };
		Random rand = new Random();
		int res = rand.nextInt(strArr.length);
		System.out.println("Displaying a random string = " + strArr[res]);
	}
}

Generate random values that won’t repeat in Java

java8

import java.util.ArrayList;
import java.util.HashSet;
import java.util.Set;
import java.util.Random;
import java.util.List;
public class Demo {
	public static void main(String[] args) {
		Random randNum = new Random();
		Set<Integer>s = new HashSet<Integer>();
		while (s.size() < 10) {
			s.add(randNum.nextInt());
		}
		System.out.println("Random numbers that aren't repeating...");
		List<Integer>list = new ArrayList<Integer>(s);
		System.out.println(list);
	}
}

Java Program to generate random numbers string

java8

public class Demo {
	static char num[] = { '0', '1', '2', '3', '4', '5' };
	public static char randomNum() {
		return num[(int) Math.floor(Math.random() * 5)];
	}
	public static void main(String[] args) {
		int len = 5;
		StringBuilder strBuilder = new StringBuilder();
		for (int i = 0; i<len; i++) {
			strBuilder.append(randomNum());
		}
		System.out.println("Random numbers string = "+strBuilder.toString());
	}
}

Convert Integer array list to float array in Java

java8

import java.util.ArrayList;
public class Demo {
	public static void main(String[] args) {
		ArrayList<Integer>arrList = new ArrayList<Integer>();
		arrList.add(25);
		arrList.add(50);
		arrList.add(100);
		arrList.add(200);
		arrList.add(300);
		arrList.add(400);
		arrList.add(500);
		final float[] arr = new float[arrList.size()];
		int index = 0;
		for (final Integer value: arrList) {
			arr[index++] = value;
		}
		System.out.println("Elements of float array...");
		for (Float i: arr) {
			System.out.println(i);
		}
	}
}

Java Program to generate a random number from an array

java8

import java.util.Random;
public class Demo {
	public static void main(String... args) {
		int[] arr = new int[] { 10, 30, 45, 60, 78, 99, 120, 140, 180, 200};
		System.out.print("Random number from the array = "+arr[new Random().nextInt(arr.length)]);
	}
}

Generate a random BigInteger value in Java

java8

import java.math.BigInteger;
import java.util.Random;
public class Demo {
	public static void main(String[] args) {
		BigInteger maxLimit = new BigInteger("5000000000000");
		BigInteger minLimit = new BigInteger("25000000000");
		BigInteger bigInteger = maxLimit.subtract(minLimit);
		Random randNum = new Random();
		int len = maxLimit.bitLength();
		BigInteger res =  new BigInteger(len, randNum);
		if (res.compareTo(minLimit) < 0)
			res = res.add(minLimit);
		if (res.compareTo(bigInteger) >= 0)
			res = res.mod(bigInteger).add(minLimit);
			System.out.println("The random BigInteger = "+res);
	}
}

Java Program to generate custom random number

java8

import java.util.Random;
public class Demo {
	public static void main(String[] args) {
		for (int i = 0; i< 5; i++) {
			Random rand = new Random();
			if (rand.nextBoolean())
				System.out.println(1);
			else
				System.out.println(-1);
		}
	}
}

Generate 10 random four-digit numbers in Java

java8

import java.util.Random;
public class Demo {
	public static void main(String[] args) {
		Random rand = new Random();
		System.out.println("Random numbers...");
		for (int i = 1; i<= 10; i++) {
			int resRandom = rand.nextInt((9999 - 100) + 1) + 10;
			System.out.println(resRandom);
		}
	}
}

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