Programming Examples

Java Program to append all elements of other Collection to ArrayList

java8

import java.util.ArrayList;
import java.util.Vector;
public class Demo {
	public static void main(String[] args) {
		ArrayList<String>arr = new ArrayList<String>();
		arr.add("50");
		arr.add("100");
		arr.add("150");
		arr.add("200");
		arr.add("250");
		arr.add("300");
		Vector<String>vector = new Vector<String>();
		vector.add("500");
		vector.add("700");
		vector.add("800");
		vector.add("1000");
		// append
		arr.addAll(vector);
		System.out.println("Result after append...");
		for (String str: arr)
			System.out.println(str);
	}
}

Insert an element to List using ListIterator in Java

java8

import java.util.ArrayList;
import java.util.ListIterator;
public class Demo {
	public static void main(String[] args) {
		ArrayList<Integer>arrList = new ArrayList<Integer>();
		arrList.add(100);
		arrList.add(200);
		arrList.add(300);
		arrList.add(400);
		arrList.add(500);
		arrList.add(600);
		arrList.add(700);
		arrList.add(800);
		ListIterator<Integer>iterator = arrList.listIterator();
		iterator.add(1000);
		iterator.add(2000);
		iterator.add(3000);
		for (Integer i: arrList){
			System.out.println(i);
		}
	}
}

Sort List in descending order using Comparator in Java

java8

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
public class Demo {
	public static void main(String[] args) {
		ArrayList<Integer>arrList = new ArrayList<Integer>();
		arrList.add(10);
		arrList.add(50);
		arrList.add(100);
		arrList.add(150);
		arrList.add(250);
		arrList.add(100);
		arrList.add(150);
		arrList.add(250);
		Comparator comparator = Collections.reverseOrder();
		System.out.println("List = "+arrList);
		Collections.sort(arrList, comparator);
		System.out.println("Sorted List in descending order = "+arrList);
	}
}

Java Program to convert LocalDate to java.util.Date

java8

import java.time.Instant;
import java.time.LocalDate;
import java.time.ZoneId;
public class Demo {
	public static void main(String[] args) {
		LocalDate date = LocalDate.now();
		System.out.println("LocalDate = "+date);
		Instant i = date.atStartOfDay().atZone(ZoneId.systemDefault()).toInstant();
		System.out.println("java.util.Date = "+java.util.Date.from(i));
	}
}

Java Program to convert LocalDateTime

java8

import java.time.Instant;
import java.time.LocalDateTime;
import java.time.ZoneId;
import java.util.Date;
public class Demo {
public static void main(String[] args) {
		LocalDateTime dateTime = LocalDateTime.now();
		Instant i = dateTime.atZone(ZoneId.systemDefault()).toInstant();
		System.out.println("Instant = "+i);
		java.util.Date date = Date.from(i);
		System.out.println("Date = "+date);
	}
}

Java Program to divide a number into smaller random ints

java8

import java.util.Arrays;
import java.util.HashSet;
import java.util.Random;
public class Demo {
	public static Random randNum = new Random();
	public static int[] DemoFunc(int number, int parts) {
		HashSet<Integer>set = new HashSet<Integer>();
		set.add(0);
		set.add(0);
		set.add(0);
		set.add(number);
		int arrSize = parts + 1;
		while (set.size() < arrSize) {
			set.add(1 + randNum.nextInt(number - 1));
		}
		Integer[] dividers = set.toArray(new Integer[arrSize]);
		Arrays.sort(dividers);
		int[] res = new int[parts];
		for(int i = 1, j = 0; i<dividers.length; ++i, ++j) {
			res[j] = dividers[i] - dividers[j];
		}
		return res;
	}
	public static void main(String[] args) {
		System.out.println(Arrays.toString(DemoFunc(10, 8)));
	}
}

Area of a triangle using Heron\'s Formula in Java

java8

public class Demo {
	public static void main(String[] args) {
		// sides of a triangle
		double s1, s2, s3;
		double area, resArea;
		// three sides of a triangle
		s1 = 15191235.0;
		s2 = 15191235.0;
		s3 = 1.01235479;
		area = (s1+s2+s3)/2.0d;
		resArea = Math.sqrt(area* (area - s1) * (area - s2) * (area - s3));
		System.out.println("Area of Triangle = " + resArea);
	}
}

Convert Integer array list to integer 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(100);
		arrList.add(200);
		arrList.add(300);
		arrList.add(400);
		arrList.add(500);
		arrList.add(600);
		arrList.add(700);
		arrList.add(800);
		arrList.add(900);
		arrList.add(1000);
		final int[] arr = new int[arrList.size()];
		int index = 0;
		for (final Integer value : arrList) {
			arr[index++] = value;
		}
		System.out.println("Elements of int array...");
		for (Integer i : arr) {
			System.out.println(i);
		}
	}
}

Sieve of Eratosthenes algorithm in Java

java8

public class Demo {
	public static void main(String[] args) {
		// set a value to check
		int val = 30;
		boolean[] isprime = new boolean[val + 1];
		for (int i = 0; i <= val; i++)
			isprime[i] = true;
			// 0 and 1 is not prime
			isprime[0] = false;
			isprime[1] = false;
			int n = (int) Math.ceil(Math.sqrt(val));
			for (int i = 0; i <= n; i++) {
				if (isprime[i])
					for (int j = 2 * i; j <= val; j = j + i)
						// not prime
						isprime[j] = false;
			}
			int myPrime;
			for (myPrime = val; !isprime[myPrime]; myPrime--)
				; // empty loop body
				System.out.println("Largest prime less than or equal to " + val + " = " + myPrime);
	}
}

Java Program to save decimal

java8

import java.math.BigDecimal;
import java.math.RoundingMode;
public class Demo {
	public static void main(String[] args) {
		double val = 320.0 / 2989.0;
		BigDecimal big = new BigDecimal(val);
		System.out.println(String.format("Value = %s", val));
		// scale
		big = big.setScale(3, RoundingMode.HALF_DOWN);
		double val2 = big.doubleValue();
		System.out.println(String.format("Scaled result = %s", val2));
	}
}

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