Java8 Programming Examples

Retrieve all the keys from HashMap in Java

java8

import java.util.HashMap;
import java.util.Iterator;
import java.util.Set;
public class Demo {
	public static void main(String[] args) {
		HashMap<Integer, String>map = new HashMap<Integer, String>();
		map.put(10, "A");
		map.put(20, "B");
		map.put(30, "C");
		map.put(40, "D");
		map.put(50, "E");
		map.put(60, "F");
		map.put(70, "G");
		map.put(80, "H");
		Set<Integer>set = map.keySet();
		Iterator<Integer>i = set.iterator();
		while (i.hasNext()) {
			Integer res = i.next();
			System.out.println(res + ": " + map.get(res));
		}
	}
}

Java Program to replace key and value in HashMap

java8

import java.util.HashMap;
import java.util.Map;
public class Demo {
	public static void main(String args[]) {
		Map<Integer, String>map = new HashMap<>();
		map.put(10, "A");
		map.put(20, "B");
		map.put(30, "C");
		map.put(40, "D");
		map.put(50, "E");
		map.put(60, "F");
		map.put(70, "G");
		map.put(80, "H");
		System.out.println("Map = \t" + map);
		map.put(30, "T");
		System.out.println("Updated Map = \t" + map);
	}
}

Java Program to remove key value pair from HashMap

java8

import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Set;
public class Demo {
	public static void main(String[] args) {
		HashMap<String,String>map = new HashMap<String,String>();
		map.put("1", "A");
		map.put("2", "B");
		map.put("3", "C");
		map.put("4", "D");
		map.put("5", "E");
		map.put("6", "F");
		map.put("7", "G");
		map.put("8", "H");
		map.put("9", "I");
		System.out.println("HashMap...");
		for (String res: map.keySet()) {
			System.out.println(res);
		}
		map.remove("5");
		System.out.println("Updated HashMap...");
		for (String res: map.keySet()) {
			System.out.println(res);
		}
		map.remove("8");
		System.out.println("Updated HashMap...");
		for (String res: map.keySet()) {
			System.out.println(res);
		}
	}
}

Java Program to display a prime number less than the given number

java8

public class Demo {
	public static void main(String[] args) {
		int val = 20;
		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 convert positive int to negative and negative to positive

java8

public class Demo {
	public static void main(String[] args) throws java.lang.Exception {
		int positiveVal = 100;
		int negativeVal = (~(positiveVal - 1));
		System.out.println("Result: Positive value converted to Negative = "+negativeVal);
		positiveVal = ~(negativeVal - 1);
		System.out.println("Actual Positive Value = "+positiveVal);
		negativeVal = -200;
		System.out.println("Actual Negative Value = "+negativeVal);
		positiveVal = ~(negativeVal - 1);
		System.out.println("Result: Negative value converted to Positive = "+positiveVal);
	}
}

Compare BigDecimal movePointRight and scaleByPowerOfTen in Java

java8

import java.math.BigDecimal;
public class Demo {
	public static void main(String... args) {
		long base = 3676;
		int scale = 5;
		BigDecimal d = BigDecimal.valueOf(base, scale);
		System.out.println("Value = "+d);
		System.out.println("\nDemonstrating moveRight()...");
		BigDecimal moveRight = d.movePointRight(12);
		System.out.println("Result = "+moveRight);
		System.out.println("Scale = " + moveRight.scale());
		System.out.println("\nDemonstrating scaleByPowerOfTen()...");
		BigDecimal scaleRes = d.scaleByPowerOfTen(12);
		System.out.println("Result = "+scaleRes);
		System.out.println("Scale = " + scaleRes.scale());
	}
}

Java Program to read map by Map.Entry

java8

import java.util.Iterator;
import java.util.Map;
import java.util.Properties;
public class Demo {
	public static void main(String[] a) {
		Properties prop = System.getProperties();
		Iterator i = prop.entrySet().iterator();
		while (i.hasNext()) {
			Map.Entry entry = (Map.Entry) i.next();
			System.out.println(entry.getKey() + " => " + entry.getValue());
		}
	}
}

Java Program to loop through Map by Map.Entry

java8

import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Set;
public class Demo {
	public static void main(String[] args) {
		HashMap<String,String>map = new HashMap<String,String>();
		map.put("1", "A");
		map.put("2", "B");
		map.put("3", "C");
		map.put("4", "D");
		map.put("5", "E");
		map.put("6", "F");
		map.put("7", "G");
		map.put("8", "H");
		map.put("9", "I");
		Set<Map.Entry<String, String>>s = map.entrySet();
		Iterator<Map.Entry<String, String>>i = s.iterator();
		while (i.hasNext()) {
			Map.Entry<String, String>e = (Map.Entry<String, String>) i.next();
			String key = (String) e.getKey();
			String value = (String) e.getValue();
			System.out.println("Key = "+key + " => Value = "+ value);
		}
	}
}

Insertion order with Java LinkedHashMap

java8

import java.util.Collection;
import java.util.Iterator;
import java.util.LinkedHashMap;
public class Demo {
	public static void main(String[] args) {
		LinkedHashMap<String,String>lHashMap = new LinkedHashMap<String,String>();
		lHashMap.put("1", "A");
		lHashMap.put("2", "B");
		lHashMap.put("3", "C");
		lHashMap.put("4", "D");
		lHashMap.put("5", "E");
		lHashMap.put("6", "F");
		lHashMap.put("7", "G");
		lHashMap.put("8", "H");
		lHashMap.put("9", "I");
		Collection collection = lHashMap.values();
		Iterator i = collection.iterator();
		while (i.hasNext()){
			System.out.println(i.next());
		}
	}
}

Extract values from HashMap in Java

java8

import java.util.HashMap;
public class Demo {
	public static void main(String args[]) {
		HashMap<Integer, Integer>m = new HashMap<Integer, Integer>();
		m.put(10, 20);
		m.put(30, 40);
		m.put(50, 60);
		m.put(70, 80);
		m.put(90, 100);
		m.put(110, 120);
		m.put(130, 140);
		m.put(150, 160);
		System.out.println("Displaying values from HashMap...");
		for (Integer i: m.keySet()) {
			System.out.println(m.get(i));
		}
	}
}

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