How to Reverse a Number in JavaIn this section, we will learn how to reverse a number in Java using while loop, for loop and recursion. To reverse a number, follow the steps given below:
Repeat the above steps until the number becomes 0. There are three ways to reverse a number in Java:
Let's apply the above steps in an example. ExampleSuppose, we want to reverse the number 1234. In this example, we have taken three variables named number (the number to be reversed), remainder (stores the remainder), reverse (stores the reverse number) initialized 0. Iteration 1:
number = 1234
remainder = 1234 % 10 = 4 reverse = 0 * 10 + 4 = 0 + 4 = 4 number = 1234 / 10 = 123 Now the value of the number and reverse variable is 123 and 4, respectively. Iteration 2:
number = 123
remainder = 123 % 10 = 3 reverse = 4 * 10 + 3 = 40 + 3 = 43 number = 123 / 10 = 12 Now the value of the number and reverse variable is 12 and 43, respectively. Iteration 3:
number = 12
remainder = 12 % 10 = 2 reverse = 43 * 10 + 2 = 430 + 2 = 432 number = 12 / 10 = 1 Now the value of the number and reverse variable is 1 and 432, respectively. Iteration 4:
number = 1
remainder = 1 % 10 = 1 reverse = 432 * 10 + 1 = 4320 + 1 = 4321 number = 1 / 10 = 0 Now the variable number become 0. Hence, we get the reverse number 4321. Let's implement the above logic in a Java program. Reverse a number using while loopReverseNumberExample1.java Output The reverse of the given number is: 456789 Reverse a number using for loopIn the following program, we have replaced the while loop by a for loop. It also removes the last digit of the number, after each iteration. When the condition, number!=0 becomes false, the loop exits and we get the reversed number. ReverseNumberExample2.java Output The reverse of the given number is: 654321 In the above program, we can also write the for loop as follows: Reverse a number using recursionReverseNumberExample3.java Output 1: Enter the number that you want to reverse: 9 The reverse of the given number is: 9 Output 2: Enter the number that you want to reverse: 7654123 The reverse of the given number is: 3214567 The following program reverses both numbers, positive and negative. When we enter a number, it first checks the number is positive or negative. If the number is negative, it converts the number into positive by multiplying 1. After that, it performs the same steps (as we have performed in the above programs) to reverse a number. At last, again it checks the number is negative or positive. To make the number negative, it again multiplies the reverse number by 1. ReverseNumberExample4.java Output 1: Enter the number that you want to reverse: 98765 The reverse of the given number is: 56789 Output 2: Enter the number that you want to reverse: 321987 The reverse of the given number is: 789123
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