Operators. Practical Tasks

Below are fourteen hands-on Java exercises on control flow: the conditional statements if, if-else, if-else-if, the switch statement, the while, do-while, for, and for-each loops, and the break, continue, and return statements plus the System.exit() method. The tasks progress from a simple even-number check to a factorial, an array search, and a properly guarded program exit. Most tasks have a ready solution on Patreon, and some also come with a video walkthrough. Before you start, we recommend reviewing the lessons on the if statement, the switch statement, loops in Java, the break and continue statements, the return statement, and the System.exit() method.

Even or Odd Number

1. Pass a number as a program argument.
2. If the number is odd, print it.
3. Use the if statement.
4. Use Integer.parseInt() to convert the String to int.

Solution on Patreon →

Number between 0 and 10

1. Use the Scanner class to read an integer.
2. If the number is between 0 (inclusive) and 10 (exclusive), print "Positive number less than 10 or zero". Otherwise, print "Positive number greater than 10 or negative".
3. Use the if-else statement.

Solution on Patreon →

Days of the Week with if-else-if

1. Pass a number from 1 to 7 as a program argument.
2. Print "Monday" if the number is 1, "Tuesday" for 2, and so on. Print "Weekend" for 6 or 7.
3. Use the if-else-if structure.

Watch the solution in the video.

Solution on Patreon →

Days of the Week with switch

Rewrite the previous task using the switch statement. Pay attention to the "6 or 7" case: in a switch it is convenient to write it as two case labels leading to the same action.

Watch the solution in the video.

Solution on Patreon →

Ten Lines with a while Loop

Print 10 lines: "Task1", "Task2", …, "Task10". Use the while loop.

Watch the solution in the video.

Solution on Patreon →

Multiples of 5 with a do-while Loop

Print all numbers from 1 to 100 that are divisible by 5 using the do-while loop.

Watch the solution in the video.

Solution on Patreon →

Five Characters with a for Loop

Print 5 characters in a row starting with 'h'. Use the for loop.

Watch the solution in the video.

Solution on Patreon →

Garland, Part 2

Extend the Garland, Part 1 task with the following:

1. Use the Scanner class to input a number from 1 to 4.
2. If the input is 1 – run the blink method, 2 – check the first bulb, 3 – run the running-light method, 4 – print the garland state to the console.
3. Use the switch statement for mode selection.
4. Update the blink method: it should blink the garland 10 times (use the for loop).
5. Update the running-light method: it should repeat the operation 10 times (use the for loop).

Solution on Patreon →

Factorial with a for Loop

Calculate the factorial using a for loop. Example:

n! = 1*2*...*n;
0! = 1;
5! = 1*2*3*4*5;

The number n is generated randomly — use (int) (Math.random() * 6). It must be in the range from 0 to 5.

Solution on Patreon →

Array Sum with a for-each Loop

1. Create an int[] array with a few numbers, for example {2, 4, 6, 8, 10}.
2. Calculate the sum of all its elements.
3. Use a for-each loop.
4. Print the result to the console.

Array Search with break

1. Create an int[] array with a few numbers and a target variable holding the number to search for.
2. Iterate over the array with a for loop.
3. As soon as the current element equals target, print its index and stop the loop immediately with the break statement.
4. If the element is not found after the loop, print "Not found".

Odd Numbers from 1 to 20 with continue

1. Set up a for loop from 1 to 20 inclusive.
2. If the current number is even, skip the iteration with the continue statement.
3. Print the remaining (odd) numbers to the console.

Primality Check with an Early return

1. Write a method public static boolean isPrime(int n).
2. Check possible divisors from 2 to n − 1.
3. As soon as a divisor is found, immediately return false with the return statement, without waiting for the loop to finish.
4. If no divisor is found, return true.
5. Call the method for a few numbers (for example, 7, 15, 23) and print the result.

Guarded Program Exit with System.exit()

1. Use the Scanner class to read an integer from the console.
2. If the number is negative, print "Error: the number must not be negative" and immediately terminate the program by calling System.exit(1).
3. If the number is non-negative, print its square to the console.