Java Internal DataStructures

import java.util.Arrays class App { public static void main(String[] args) { int[] numArr = new int[10]; for (int i = 0; i < numArr.length; i++) { numArr[i] = i * 2; } int[] numArr2 = new int[10]; for (int i = 0; i < numArr.length; i++) { numArr2[i] = 10 - i; } int[][] arr = new int[4][4]; // arr.length System.out.println("length: " + numArr.length); // toString method System.out.println("print arr : "); System.out.println(Arrays.toString(numArr)); System.out.println(Arrays.toString(numArr2)); // returns index System.out.println("index of 4 in numArr: " + Arrays.binarySearch(numArr, 4)); // to print 2D array as string System.out.println("deepToString() : "); System.out.println(Arrays.deepToString(arr)); // to sort array Arrays.sort(numArr2); System.out.println(Arrays.toString(numArr2)); // to calc sum : convert to stream System.out.println("Sum: " + Arrays.stream(numArr).sum()); } } 

import java.util.ArrayList; import java.util.Arrays; class App { public static void main(String[] args) { ArrayList<Integer> arrlst = new ArrayList<>(); for (int i = 0; i < 10; i++) { arrlst.add(i); } System.out.println(arrlst.toString()); // size to arrlst System.out.println("Size: " + arrlst.size()); // get element from index arrlst System.out.println("index: " + arrlst.get(3)); // arrlst isEmpty ? System.out.println("isEmpty : " + arrlst.isEmpty()); // add one element arrlst.add(10); ArrayList<Integer> arrlst2 = new ArrayList<>(); arrlst2.add(11); arrlst2.add(12); // addAll arrlst.addAll(arrlst2); System.out.println(arrlst.toString()); System.out.println(arrlst2.toString()); // clear arrlst2.clear(); // contains System.out.println(arrlst.contains(13) + " " + arrlst.contains(1)); // indexOf System.out.println("indexof: " + arrlst.indexOf(6)); // remove System.out.println("element removed: " + arrlst.remove(6)); System.out.println(arrlst.toString()); // set arrlst.set(2, 4); System.out.println(arrlst.toString()); // sort arrlst.sort(null); System.out.println(arrlst.toString()); // toArray var something = arrlst.toArray(); System.out.println(Arrays.toString(something)); } } 

public class App { public static void main(String[] args) { Stack<Integer> stck = new Stack<>(); try { stck.peek(); } catch (Exception e) { System.out.println("if stack is empty, then peek throws an exception"); } stck.push(1); stck.push(2); stck.push(3); System.out.println(stck.pop()); System.out.println(stck.peek()); System.out.println(stck.isEmpty()); System.out.println(stck.isEmpty()); System.out.println(stck.size()); } } 

public class App { public static void main(String[] args) { Queue<Integer> queue = new LinkedList<>(); queue.add(1); queue.add(2); queue.add(3); queue.add(4); // throws exception when queue is empty System.out.println(queue.remove()); // returns null when queue is empty System.out.println(queue.poll()); System.out.println(queue.peek()); // if queue under capacity then offer returns true else returns false System.out.println(queue.offer(6)); System.out.println(queue.toString()); } } 

public class App { public static void main(String[] args) { Set<Integer> set = new HashSet<>(); set.add(1); set.add(2); set.add(3); System.out.println(set.contains(2)); System.out.println(set.remove(3)); System.out.println(set.isEmpty()); System.out.println(set.isEmpty()); System.out.println(set.toString()); } } 

public class App { public static void main(String[] args) { Map<Integer,String> hmap = new HashMap<>(); hmap.put(1,"uday yadav"); hmap.putIfAbsent(2,"uday yadav"); hmap.putIfAbsent(2,"another uday"); hmap.putIfAbsent(3,"yadav uday"); System.out.println(hmap.containsKey(2)); hmap.getOrDefault(6,""); hmap.remove(3); System.out.println(hmap.toString()); hmap.size(); hmap.clear(); System.out.println(hmap.toString()); } }