Output formatting basics in Java - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print "Hello, World!" to the console.

Java

System.out.[1]("Hello, World!");

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

Aoutput

Bprintln

Cwrite

Dprint

Attempts:

3 left

💡 Hint

Common Mistakes

Using print instead of println, so output stays on the same line.

Trying to use a method that doesn't exist like write or output.

The println method prints the text and moves to a new line.

2fill in blank

medium

Complete the code to format and print a floating-point number with two decimal places.

Java

System.out.printf("%.[1]f", 3.14159);

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A3

B1

C4

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1 or 3 decimals instead of 2.

Forgetting the 'f' in the format specifier.

The %.2f format specifier prints a floating-point number with two decimals.

3fill in blank

hard

Fix the error in the code to print an integer padded with zeros to width 5.

Java

System.out.printf("%[1]d", 42);

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A05

B5

C-5

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using just 5 without zero, which pads with spaces.

Using negative width which left-aligns but doesn't pad zeros.

The format specifier %05d pads the integer with zeros to make it 5 characters wide.

4fill in blank

hard

Fill both blanks to print a string left-aligned in a field of width 10.

Java

System.out.printf("%[1][2]s", "Hi");

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A-

B+

C10

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' which is not valid for string alignment.

Using width 5 which is too small for the example.

The %-10s format specifier prints the string left-aligned in a 10-character wide field.

5fill in blank

hard

Fill all three blanks to print a floating-point number right-aligned with width 8 and 3 decimals.

Java

System.out.printf("%[1][2][3]f", 7.12345);

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A-

B8

C.3

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-' which left-aligns instead of right-aligning.

Forgetting the dot before the decimal count.

The format specifier %08.3f prints the number padded with zeros, width 8, and 3 decimals.

Practice

1. Which Java method is commonly used to format output with placeholders like %d or %s?

easy

A. System.out.read

B. System.out.printf

C. System.out.println

D. System.out.print

Solution

1. Step 1: Identify formatting methods in Java

   System.out.printf and System.out.format are used for formatted output, unlike println or print which just print raw text.

2. Step 2: Recognize the method that uses placeholders

   System.out.printf uses format specifiers like %d for integers and %s for strings to format output.

3. Final Answer:

   System.out.printf -> Option B

4. Quick Check:

   Formatted output uses printf [OK]

Hint: Look for method with % placeholders for formatting [OK]

Common Mistakes:

• Confusing println with printf
• Using print which lacks formatting
• Thinking read formats output

2. Which of the following is the correct syntax to print an integer variable num with two digits padded with zeros using printf?

easy

A. System.out.printf("%02d", num);

B. System.out.printf("%2d", num);

C. System.out.printf("%d2", num);

D. System.out.printf("%d02", num);

Solution

1. Step 1: Understand zero-padding format specifier

   In printf, %02d means print an integer padded with zeros to width 2.

2. Step 2: Check each option's correctness

   %2d pads with spaces, %02d pads with zeros, %d2 and %d02 are invalid formats.

3. Final Answer:

   System.out.printf("%02d", num); -> Option A

4. Quick Check:

   Zero padding uses %0Nd [OK]

Hint: Zero pad with %0 before width number [OK]

Common Mistakes:

• Using %2d pads with spaces, not zeros
• Placing digits after %d incorrectly
• Confusing padding syntax

3. What is the output of the following Java code?

int x = 7;
System.out.printf("Value: %4d!", x);

medium

A. Value: 7!

B. Value: 7 !

C. Value: 07!

D. Value:7!

Solution

1. Step 1: Understand %4d formatting

   %4d means print integer right-aligned in a field width of 4 characters, padding with spaces on the left.

2. Step 2: Apply formatting to value 7

   7 is one digit, so 3 spaces are added before it, resulting in " 7".

3. Final Answer:

   Value: 7! -> Option A

4. Quick Check:

   Right-align integer in 4 spaces [OK]

Hint: Width number pads spaces on left for integers [OK]

Common Mistakes:

• Assuming padding is on the right
• Confusing zero padding with space padding
• Ignoring field width

4. The following code is intended to print a floating-point number with 2 decimal places:

double pi = 3.14159;
System.out.printf("%.2f", pi);

What is the error in this code?

medium

A. Missing newline character causes error.

B. %.2f is invalid format specifier for double.

C. No error; it prints 3.14 correctly.

D. Must cast pi to float before printing.

Solution

1. Step 1: Check format specifier for double

   %.2f formats floating-point numbers with 2 decimal places, valid for double type.

2. Step 2: Verify code correctness

   Code prints 3.14 without error; newline is optional and casting is unnecessary.

3. Final Answer:

   No error; it prints 3.14 correctly. -> Option C

4. Quick Check:

   %.2f formats double with 2 decimals [OK]

Hint: %.Nf formats float/double to N decimals [OK]

Common Mistakes:

• Thinking casting to float is needed
• Assuming newline is mandatory
• Believing %.2f is invalid

5. You want to print a table of names and ages aligned in columns using printf. Which format string correctly aligns the name left in 10 spaces and age right in 3 spaces?

String name = "Anna";
int age = 9;
System.out.printf("???", name, age);

hard

A. "%-3s %-10d"

B. "%10s %-3d"

C. "%10s %3d"

D. "%-10s %3d"

Solution

1. Step 1: Understand alignment flags in printf

   %-10s means left-align string in 10 spaces; %3d means right-align integer in 3 spaces.

2. Step 2: Match format to requirement

   "%-10s %3d" matches left-align name and right-align age correctly; others swap or misalign.

3. Final Answer:

   "%-10s %3d" -> Option D

4. Quick Check:

   Left-align string with - flag, right-align number default [OK]

Hint: Use %- for left-align strings, default right-align numbers [OK]

Common Mistakes:

• Swapping alignment flags
• Using wrong width numbers
• Misplacing % signs