Useful Java Code Snippets 1 - Collections Framework (Lists, Arraylists, Hashsets,..)



Looking for useful code examples to build your Java applications? 


Java is one of the best programming languages from which to build rich applications from scratch. Developed in the early 1980s by the team at Sun Microsystems, Java has become crucial for the industry. Here I am going to post free Java code examples for developers..


The Java Collections Framework is a collection of interfaces and classes which provides an efficient data processing. This framework has numerous useful classes which have very useful functions which makes a programming task incredibly easy.





1 - ArrayLists & Comparison using hasNext() Method

/**
* Author : Berk Soysal
* UsefulCodes.java
*/

import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;

public class UsefulCodes {
  
  // ArrayLists
  public static List<String> listeler(int a){
    String[] words2={"eggs","lazers","hats","pie"};
    String[] words3={"lazers","hats"};
    
    List<String> list = new ArrayList<>();
    List<String> list2 = new ArrayList<>();
    
    //add array items to the list
    for(String x: words2)
      list.add(x);
    
    for(String y: words3)
      list2.add(y);
    
    if(a==1)return list;
    else return list2;
  }
  
  //editList
  public static void editList(Collection<String> l1, Collection<String> l2){
    
    Iterator<String> it = l1.iterator();
    while(it.hasNext()){
      if(l2.contains(it.next()))
        it.remove();
    }
    System.out.println(l1.toString());
    
  }
  
  // Main Method
  public static void main(String[] args) {
    // Compares 2 lists and excludes the identical elements //from the first list
    editList(listeler(1),listeler(2));
  }
}




2 - LinkedLists Editing and Reversing

/**
* Author : Berk Soysal
* UsefulCodes.java
*/

import java.util.LinkedList;
import java.util.List;


public class UsefulCodes {
  
  // LinkedLists
  public static void linkedlisteler(){
    
    String[] words={"funk","chunk","furry","terminator"};
    String[] words2={"trunk","goats","harry","potter"};
    List<String> list= new LinkedList<String>();
    List<String> list2= new LinkedList<String>();
    for(String x : words)
      list.add(x);
    for(String y : words2)
      list2.add(y);
    
    list.addAll(list2);
    list2=null; // clear the allocated memory for list2
    
    //Print the list
    System.out.printf(" Original List: ");
    for(String z: list)
      System.out.printf("%s ",z);
    //Remove first two elements from the list
    list.remove(0);
    //Since this is a linked list it shifts to the left
    list.remove(0);
    
    //Print the edited list
    System.out.printf("\n Edited List: ");
    for(String z: list)
      System.out.printf("%s ",z);
    
    //Reverse the list 
    System.out.printf("\n Reversed List: ");
    for(int i=list.size()-1;i>=0;i--)
      System.out.printf( list.get(i)+ " ");
    
  }
  
  // Main Method
  public static void main(String[] args) {
    linkedlisteler();
  }
}



3 - Array-to-List & List-to-Array Conversions

/**
* Author : Berk Soysal
* UsefulCodes.java
*/

import java.util.Arrays;
import java.util.LinkedList;


public class UsefulCodes {
  
  // Array-to-List & List-to-Array Conversions 
  public static void converter(){
    String[] stuff = {"cookies", "watermelon","olive","zucchini"};
    LinkedList<String> thelist = new LinkedList<String>(Arrays.asList(stuff));
    
    
    thelist.add("LAST");
    thelist.addFirst("FIRST");
    
    // convert back to an array
    stuff= thelist.toArray(new String[thelist.size()]);
    
    for( String z: stuff)
      System.out.printf(" %s",z);
    
  }
  
  // Main Method
  public static void main(String[] args) {
    converter();
  }
}



 4 - Collections and addAll() Method

/**
* Author : Berk Soysal
* UsefulCodes.java
*/

import java.util.ArrayList;
import java.util.Collections;


public class UsefulCodes {
  
  //Collections and addAll() Method
  public static void collection(){
    String[] stuff = {"chocolate", "pizza","bread","rice"};
    
    ArrayList<String> list = new ArrayList<String>();
    list.add("youtube");
    list.add("google");
    list.add("outlook");
    
    System.out.printf("Collection = ");
    
    for(String z : list)
      System.out.printf("%s ",z);
    
    // Add all elements from stuff to List2
    Collections.addAll(list,stuff);
    
    System.out.printf("\nNew Collection = ");
    for(String z : list)
      System.out.printf("%s ",z);
    
  }
  
  // Main Method
  public static void main(String[] args) {
    collection();
  }
}



5 - Stacks - Push & Pop Operations

/**
* Author : Berk Soysal
* UsefulCodes.java
*/

import java.util.Stack;

public class UsefulCodes {
  
  // STACKS, PUSH, POP
  public static void stacks(){
    
    Stack<String> stack = new Stack<String>();
    stack.push("Bottom");
    printStack(stack);
    stack.push("Second");
    printStack(stack);
    stack.push("Third");
    printStack(stack);
    //The last one goes in, goes out first when "pop" is used
    stack.pop();
    printStack(stack);
  }
  
  private static void printStack(Stack<String> s){
    if(s.isEmpty()) System.out.println("Empty Stack !");
    else System.out.printf("%s TOP of the Stack \n",s);
  }
  
  // Main Method
  public static void main(String[] args) {
    stacks();
  }
}




6 - Priority Queues

/**
* Author : Berk Soysal
* UsefulCodes.java
*/

import java.util.PriorityQueue;

public class UsefulCodes {
  
  // Queues
  private static void queues(){
    PriorityQueue<String> q = new PriorityQueue<String>();
    q.offer("First");
    q.offer("Second");
    q.offer("Third");
    
    System.out.println(q);
    
    // Remove the highest priority element
    q.poll();
    System.out.println(q);
    
  }
  
  // Main Method
  public static void main(String[] args) {
    queues();
  }
}




7 - HashSets

/**
* Author : Berk Soysal
* UsefulCodes.java
*/

import java.util.Arrays;
import java.util.HashSet;
import java.util.List;
import java.util.Set;


public class UsefulCodes {
  
  //Sets
  private static void hashSet(){
    String[] stuff = {"chocolate", "pizza","bread","pizza","rice","rice","bread","chocolate"};
    List<String> list = Arrays.asList(stuff);
    System.out.println(list);
    
    Set<String> set = new HashSet<>(list);
    System.out.println(set);
    // Sets have unique elements only !
  }
  
  // Main Method
  public static void main(String[] args) {
    hashSet();
  }
}


Continue Reading Useful Java Code Snippets 2 - Generic Methods

Author:

Software Developer, Codemio Admin


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