Why operators are needed in Java - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add two numbers and print the result.

Java

int a = 5;
int b = 3;
int sum = a [1] b;
System.out.println(sum);

Drag options to blanks, or click blank then click option'

A/

B-

C*

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction or multiplication instead of addition.

The plus operator + adds two numbers together.

2fill in blank

medium

Complete the code to check if a number is greater than 10.

Java

int number = 15;
boolean isGreater = number [1] 10;
System.out.println(isGreater);

Drag options to blanks, or click blank then click option'

A>

B<

C==

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using less than or equals instead of greater than.

The greater than operator > checks if the left value is bigger than the right.

3fill in blank

hard

Fix the error in the code to multiply two numbers correctly.

Java

int x = 4;
int y = 6;
int product = x [1] y;
System.out.println(product);

Drag options to blanks, or click blank then click option'

A+

B*

C-

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using plus or minus instead of multiplication.

The multiplication operator * multiplies two numbers.

4fill in blank

hard

Fill both blanks to create a condition that checks if a number is between 5 and 10 (inclusive).

Java

int num = 7;
boolean isBetween = num [1] 5 && num [2] 10;
System.out.println(isBetween);

Drag options to blanks, or click blank then click option'

A>=

B<

C<=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using only > or < which excludes the boundary numbers.

The operator >= means 'greater than or equal to', and <= means 'less than or equal to'. Together they check if the number is between 5 and 10 inclusive.

5fill in blank

hard

Fill the blanks to create a map of words to their lengths, including only words longer than 3 characters.

Java

Map<String, Integer> lengths = words.stream()
    .filter(word -> word.length() [1] 3)
    .collect(Collectors.toMap(word -> word, word -> word.[2]()));

Drag options to blanks, or click blank then click option'

A>

Blength

Dsubstring

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong comparison operators or wrong methods for length.

The filter uses > to keep words longer than 3. The key mapper uses word itself, and the value mapper uses length() to get the word length.

Practice

1. Why do we need operators in Java programming?

easy

A. To perform calculations and compare values

B. To create new classes

C. To write comments in code

D. To define the program's main method

Solution

1. Step 1: Understand the role of operators

   Operators are symbols that perform operations like addition, subtraction, or comparison on values.

2. Step 2: Identify what operators enable

   They allow the program to calculate results and make decisions based on comparisons.

3. Final Answer:

   To perform calculations and compare values -> Option A

4. Quick Check:

   Operators = calculations and comparisons [OK]

Hint: Operators do math and comparisons in code [OK]

Common Mistakes:

• Thinking operators create classes
• Confusing operators with comments
• Believing operators define methods

2. Which of the following is the correct way to use the addition operator in Java?

easy

A. int sum = 5 plus 3;

B. int sum = 5 add 3;

C. int sum = 5 & 3;

D. int sum = 5 + 3;

Solution

1. Step 1: Recognize the addition operator syntax

   In Java, the plus sign (+) is used to add two numbers.

2. Step 2: Check each option for correct syntax

   int sum = 5 + 3; uses '+' correctly; others use invalid keywords or symbols.

3. Final Answer:

   int sum = 5 + 3; -> Option D

4. Quick Check:

   Use '+' for addition [OK]

Hint: Use '+' symbol for addition in Java [OK]

Common Mistakes:

• Using words like 'plus' instead of '+'
• Using bitwise '&' instead of '+'
• Writing invalid keywords like 'add'

3. What will be the output of this Java code?

int a = 10;
int b = 3;
int result = a / b;
System.out.println(result);

medium

A. 3

B. 4

C. 3.3333

D. Error

Solution

1. Step 1: Understand integer division in Java

   Dividing two integers results in an integer by dropping the decimal part.

2. Step 2: Calculate 10 divided by 3 as integer division

   10 / 3 equals 3 with remainder 1, but remainder is discarded.

3. Final Answer:

   3 -> Option A

4. Quick Check:

   Integer division truncates decimals [OK]

Hint: Integer division drops decimals, so 10/3 = 3 [OK]

Common Mistakes:

• Expecting decimal result from integer division
• Confusing division operator with modulo
• Thinking code causes error

4. Find the error in this Java code snippet:

int x = 5;
int y = 10;
if (x = y) {
    System.out.println("Equal");
}

medium

A. Missing semicolon after if statement

B. Using '=' instead of '==' in if condition

C. Variables x and y are not declared

D. Print statement syntax is wrong

Solution

1. Step 1: Check the if condition syntax

   The '=' operator assigns value; '==' compares values in conditions.

2. Step 2: Identify the mistake in the condition

   Using '=' tries to assign y to x, which is invalid in if condition and causes error.

3. Final Answer:

   Using '=' instead of '==' in if condition -> Option B

4. Quick Check:

   Use '==' to compare values in if [OK]

Hint: Use '==' for comparison, '=' is assignment [OK]

Common Mistakes:

• Confusing assignment '=' with comparison '=='
• Thinking semicolon needed after if condition
• Assuming variables are undeclared

5. You want to check if a number is between 10 and 20 (inclusive) in Java. Which operator combination correctly does this?

int num = 15;
if ( ? ) {
    System.out.println("In range");
}

hard

A. num == 10 && num == 20

B. num > 10 || num < 20

C. num >= 10 && num <= 20

D. num >= 10 || num <= 20

Solution

1. Step 1: Understand the range condition

   Number must be greater than or equal to 10 AND less than or equal to 20.

2. Step 2: Identify correct logical operators

   '&&' means both conditions must be true; '>=' and '<=' check inclusive bounds.

3. Final Answer:

   num >= 10 && num <= 20 -> Option C

4. Quick Check:

   Use '&&' for both conditions true [OK]

Hint: Use '&&' to combine conditions for range checks [OK]

Common Mistakes:

• Using '||' which allows out-of-range values
• Checking equality to both ends simultaneously
• Confusing inclusive and exclusive operators