Java8 Programming Examples

Create Java Priority Queue to ignore duplicates

java8

import java.util.HashSet;
import java.util.PriorityQueue;
public class Demo {
	public static void main(String[] args) {
		HashSet<Integer>set = new HashSet<>();
		set.add(100);
		set.add(150);
		set.add(250);
		set.add(300);
		set.add(250);
		set.add(500);
		set.add(600);
		set.add(500);
		set.add(900);
		PriorityQueue<Integer>queue = new PriorityQueue<>(set);
		System.out.println("Elements with no duplicates = "+queue);
	}
}

Create a read-only list in Java

java8

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
public class Demo {
	public static void main(String args[]) throws Exception {
		List<String>list = new ArrayList<String>();
		list.add("A");
		list.add("B");
		list.add("C");
		list = Collections.unmodifiableList(list);
		// An exception is thrown since its a read-only list now
		list.add("D");
		list.add("E");
		list.add("F");
		System.out.println(list);
	}
}

Java Program to create a new list with values from existing list

java8

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.function.Function;
import java.util.stream.Collectors;
public class Demo {
	public static void main(String args[]) {
		List<Employee>emp = Arrays.asList(new Employee("Jack", 29, "South"), new Employee("Tom", 24, "North"), new Employee("Harry", 35, "West"),new Employee("Katie", 32, "East"));
		List<String>res =  emp.stream().map(u ->u.displayEmpName()).collect(Collectors.toList());
		System.out.println("Employee Names = "+res);
	}
}
class Employee {
	private String emp_name;
	private int emp_age;
	private String emp_zone;
	public Employee(String emp_name, int emp_age, String emp_zone) {
		this.emp_name = emp_name;
		this.emp_age = emp_age;
		this.emp_zone = emp_zone;
	}
	public String displayEmpName() {
		return this.emp_name;
	}
}

Java Program to create a new list

java8

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.function.Function;
public class Demo {
	public static void main(String args[]) {
		List < Employee > emp = Arrays.asList(new Employee("Jack", 29, "South"), new Employee("Tom", 24, "North"), new Employee("Harry", 35, "West"), new Employee("Katie", 32, "East"));
		List < String > res = processElements(emp, p -> p.displayEmpName());
		System.out.println("Employee Names + " + res);
	}
	public static < X, Y > List < Y > processElements(Iterable < X > src,
	Function < X, Y > mapper) {
		List < Y > list = new ArrayList <> ();
		for (X p: src)
		list.add(mapper.apply(p));
		return list;
	}
}
class Employee {
	private String emp_name;
	private int emp_age;
	private String emp_zone;
	public Employee(String emp_name, int emp_age, String emp_zone) {
		this.emp_name = emp_name;
		this.emp_age = emp_age;
		this.emp_zone = emp_zone;
	}
	public String displayEmpName() {
		return this.emp_name;
	}
}

Create an unmodifiable map in Java

java8

import java.util.*;
public class Demo {
	public static void main(String[] s) {
		Hashtable<String,String>hash = new Hashtable<String,String>();
		hash.put("key1", "value1");
		hash.put("key2", "value2");
		hash.put("key3", "value3");
		System.out.println("Initial collection: "+hash);
		Map map= Collections.unmodifiableMap(hash);
		// error will generate
		map.put("key3", "value3");
	}
}

Java Program to copy value from one list to another list

java8

import java.util.ArrayList;
import java.util.Collections;
import java.util.LinkedList;
import java.util.List;
import java.util.ListIterator;
public class Demo {
	public static void main(String[] args) {
		String[] str = { "P", "Q", "R", "S", "T", "U", "V", "W" };
		int len = str.length;
		List<String>list1 = new ArrayList<String>();
		for (int i = 0; i<len; i++)
			list1.add(str[i]);
			List<String>list2 = new ArrayList<String>();
		for (int i = 0; i<len; i++)
			list2.add("");
			Collections.copy(list2,list1);
			ListIterator<String>iterator = list2.listIterator();
			System.out.println("New List...");
		while (iterator.hasNext())
			System.out.println(iterator.next());
	}
}

Java Program to add and remove elements in set

java8

import java.util.LinkedHashSet;
public class Demo {
	public static void main(String[] args) {
		LinkedHashSet<Integer>set = new LinkedHashSet<Integer>();
		set.add(20);
		set.add(60);
		set.add(80);
		set.add(120);
		set.add(150);
		set.add(200);
		set.add(220);
		set.add(260);
		set.add(380);
		System.out.println("Set = "+set);
		set.remove(150);
		set.remove(260);
		System.out.println("Updated Set = "+set);
		set.remove(60);
		System.out.println("Updated Set = "+set);
	}
}

Create a Queue from LinkedList in Java

java8

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;
public class Demo {
	public static void main(String[] args) {
		Queue<String>queue = new LinkedList<String>();
		queue.add("P");
		queue.add("Q");
		queue.add("R");
		queue.add("S");
		queue.add("T");
		queue.add("U");
		queue.add("V");
		List<String>list = new ArrayList<String>(queue);
		for (Object ob: list)
		 System.out.println(ob);
	}
}

Java Program to convert Properties list into a Map

java8

import java.util.HashMap;
import java.util.Map;
import java.util.Properties;
import java.util.Set;
public class Demo {
	public static void main(String args[]) {
		Properties p = new Properties();
		p.setProperty("P", "1");
		p.setProperty("Q", "2");
		p.setProperty("R", "3");
		p.setProperty("S", "4");
		p.setProperty("T", "5");
		p.setProperty("U", "6");
		p.setProperty("V", "7");
		HashMap<String, String>map = new HashMap<String, String>((Map) p);
		Set<Map.Entry<String, String>>set =  map.entrySet();
		System.out.println("Key and Value of the Map... ");
		for (Map.Entry<String, String>m: set) {
			System.out.print(m.getKey() + ": ");
			System.out.println(m.getValue());
		}
	}
}

Java Program to get Tail Map from TreeMap

java8

import java.util.SortedMap;
import java.util.TreeMap;
public class Demo {
	public static void main(String[] args) {
		TreeMap<String, String>tMap = new TreeMap<String,String>();
		tMap.put("1", "A");
		tMap.put("2", "B");
		tMap.put("3", "C");
		tMap.put("4", "D");
		tMap.put("5", "E");
		tMap.put("6", "F");
		tMap.put("7", "G");
		tMap.put("8", "H");
		tMap.put("9", "I");
		tMap.put("10", "J");
		SortedMap map = tMap.tailMap("2");
		System.out.println("Sub Map = " + map);
		map = tMap.tailMap("8");
		System.out.println("Sub Map = " + map);
		map = tMap.tailMap("1");
		System.out.println("Sub Map = " + map);
	}
}

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