Play with Java Arrays & Patterns

Arrays & Patterns — Sounds interesting? or complicated? Let’s find out..

There are lots of resources available online and I thought to put all together for the ease of use. Hope it will help you too :)

A simple online compiler will help you to try out : https://www.programiz.com/java-programming/online-compiler/

Basics on How to..

• Declare an array

int[] a = new int[]{45, 12, 78, 34, 89, 21};  //method 1

String[] cars = {"Volvo", "BMW", "Ford", "Mazda"};  //method 2

• Print an array

String[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
System.out.println(cars[0]);  //will print the value of 0th index

//output : Volvo

• Get Array length

String[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
System.out.println(cars.length);

//output : 4

Here are some interesting and commonly practiced algorithms

• Sort an Integer Array using “Arrays” util

import java.util.Arrays;
public class MyClass {

  public static void main(String args[]) {
    int[] a = new int[] {45,12,78,34,89,21};
    Arrays.sort(a);
    System.out.print(Arrays.toString(a));
  }
}

//output : [12, 21, 34, 45, 78, 89]

• Reverse a string input using “Scanner” util

import java.util.Scanner;
public class Main {
  public static void main(String[] args) {
    System.out.println("Enter string to reverse:");

    Scanner read = new Scanner(System.in);
    String str = read.nextLine();
    String reverse = "";

    for (int i = str.length() - 1; i >= 0; i--) {
      reverse = reverse + str.charAt(i);
    }

    System.out.println("Reversed string is:");
    System.out.println(reverse);
  }
}


/* output:

Enter string to reverse:
Automation
Reversed string is:noitamotuA

*/

• Reverse String without using utils

String rev = "";
String str = "Automation";
for (int i = str.length(); i > 0; --i) {
  rev = rev + (str.charAt(i - 1));
}
System.out.print(rev);

//output: noitamotuA

• Reverse an Int array

int[] arr = {10,20,30,40,50};
int[] b = new int[arr.length];

int j = arr.length;
for (int i = 0; i < arr.length; i++) {
  b[j - 1] = arr[i];
  j = j - 1;
}

// printing the reversed array
for (int k = 0; k < arr.length; k++) {
  System.out.print(b[k] + " ");
}

//output: 50 40 30 20 10

• Print Max number

 int[] myNum = {2,1,10,5,3,8};
 int max = 0;

 for (int i = 0; i < myNum.length; i++) {
   if (myNum[i] > max) {
     max = myNum[i];
   }
 }
 System.out.print(max);

//output: 10

• Return true if number is present

int[] myNum = {2,1,10,5,3,8};

int a = 99; // Enter the value to check

boolean result = false;
for (int i = 0; i < myNum.length; i++) {
  if (myNum[i] == a) {
    result = true;
    break;
  }

}
System.out.print(result);

//output: false

• Print the multiplication for 10 items for given int

int c = 10;
int i = c++;

for (int a = 1; a <= 10; a++) {
  int j = i * a;
  System.out.println(i + "*" + a + "=" + j);
}

/* output:

Enter number:10
10*1=10
10*2=20
10*3=30
10*4=40
10*5=50
10*6=60
10*7=70
10*8=80
10*9=90
10*10=100

*/

• Print the multiplication for 10 items for given int using “Scanner” util

import java.util.Scanner;
public class Main {
  public static void main(String[] args) {

    System.out.println("Enter number:");
    Scanner in = new Scanner(System.in);
    int i = in.nextInt();
    for (int a = 1; a <= 10; a++) {
      int j = i * a;
      System.out.println(i + "*" + a + "=" + j);
    }

  }
}

/* output:

Enter number:10
10*1=10
10*2=20
10*3=30
10*4=40
10*5=50
10*6=60
10*7=70
10*8=80
10*9=90
10*10=100

*/

• Find the number of occurrences

String text = "automation";
char someChar = 'a'; //Enter the char 
int count = 0;

for (int i = 0; i < text.length(); i++) {
  if (text.charAt(i) == someChar) {
    count++;
  }
}
System.out.println(count + " Occurrences found for the word '" + text + "'");


//output:  2 Occurrences found for the word 'automation'

• Find duplicates in an Array

 int[] arr = new int[] {1,2,5,5,6,6,7,2};

 for (int a = 0; a < arr.length; a++) {

   for (int i = a + 1; i < arr.length; i++) {
     if (arr[a] == arr[i])
       System.out.println("Duplicate Element :" + arr[a]);
   }
 }

//output 
Duplicate Element :2
Duplicate Element :5
Duplicate Element :6

• Largest number in an Array

 int[] myNum = {2,1,10,5,3,8};

 int largest = 0;
 for (int n: myNum) {
   if (n > largest) {
     largest = n;
   }
 }
 System.out.println("Largest :" + largest);

//output: Largest :10

• Second largest in an Array

int[] myNum = {2,1,10,5,3,8};

int largest = 0;
int secondLargest = 0;

for (int n: myNum) {
  if (n > largest) {
    secondLargest = largest;
    largest = n;
  } else if (n > secondLargest) {
    secondLargest = n;
  }
}
System.out.println("Largest :" + largest);
System.out.println("Second Largest :" + secondLargest);

//output: Largest :10 Second Largest :8

• Remainder

int[] myNum = {2,1,10,5,3,8};

int remainder;

for (int i = 0; i < myNum.length; i++) {
  remainder = myNum[i] % 2;
  System.out.println("Remainder :" + remainder);
}

//output: 
Remainder :0
Remainder :1
Remainder :0
Remainder :1
Remainder :1
Remainder :0

• Star Pattern

for (int i = 0; i <= 5; i++) {
  for (int j = 0; j < i; j++) {
    System.out.print("*");
  }
  System.out.println("");
}

//output
*
**
***
****
*****

• Number Pattern

for (int i = 0; i <= 5; i++) {
   for (int j = 0; j < i; j++) {
     System.out.print(i);
   }
   System.out.println();
 }


//output
1
22
333
4444
55555

There are many more but will stop here for now :) Leave a comment if there’s something I’ve missed. Love to hear from you..

Stay tuned for my next article on “Printing Patterns in Java”.

Happy Learning!