Arrays
-
arr.length : int
- returns the length of array
.toString(arr) : String
-
binarySearch(arr, (Object) key) : int
- return negative if not found
- else return index of the key
.deepToString(arr[][]) : for 2d array
-
sort(arr) : void
- Sorts the array
.stream(arr).sum() : int
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());
}
}
List : ArrayList
- arr.size() : int
- arr.get(index) : int
- arr.isEmpty() : boolean
- arr.add(Object) : boolean
- arr.addAll(Collections)
- arr.clear() : void
- arr.contains(Object) : boolean
- arr.indexOf(Object) : int
- arr.remove(index) : int
- arr.sort(null)
- arr.toArray() : Object[]
- arr.set(index, element)
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));
}
}
Stack
- pop
- push
- peek
- empty
- size
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());
}
}
Queue
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());
}
}
Set
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());
}
}
Map
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());
}
}
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