String comparison in Java - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to compare two strings for equality.

Java

String a = "hello";
String b = "hello";
boolean result = a.[1](b);

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

AequalsIgnoreCase

B==

CcompareTo

Dequals

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' operator which compares references, not content.

The equals method compares the content of two strings for equality.

2fill in blank

medium

Complete the code to compare two strings ignoring case differences.

Java

String a = "Hello";
String b = "hello";
boolean result = a.[1](b);

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

AcompareTo

Bequals

CequalsIgnoreCase

DstartsWith

Attempts:

3 left

💡 Hint

Common Mistakes

Using equals which is case-sensitive.

The equalsIgnoreCase method compares two strings ignoring case differences.

3fill in blank

hard

Fix the error in the code to correctly compare two strings.

Java

String a = "test";
String b = new String("test");
if (a.[1](b)) {
    System.out.println("Equal");
} else {
    System.out.println("Not equal");
}

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

A==

Bequals

C!=

DcompareTo

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' operator which compares object references.

Use equals to compare string contents, not == which compares references.

4fill in blank

hard

Fill both blanks to create a map of strings to their lengths, but only include strings longer than 3 characters.

Java

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

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

Alength

Blength()

Dsize()

Attempts:

3 left

💡 Hint

Common Mistakes

Using length without parentheses which is a field for arrays, not strings.

Using size() which is for collections, not strings.

The length() method returns the length of a string. It is used both to filter and to get the length value.

5fill in blank

hard

Fill all three blanks to create a map of uppercase strings to their lengths, including only strings longer than 4 characters.

Java

Map<String, Integer> result = words.stream()
    .filter(word -> word.[1]() > 4)
    .collect(Collectors.toMap(word -> word.[2](), word -> word.[3]()));

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

Alength()

BtoUpperCase()

DtoLowerCase()

Attempts:

3 left

💡 Hint

Common Mistakes

Using length without parentheses.

Using toLowerCase() instead of toUpperCase().

Use length() to filter by length, toUpperCase() to convert strings to uppercase for keys, and length() again to get the length values.

Practice

1. Which method should you use in Java to check if two strings have exactly the same characters and case?
String s1 = "Hello";
String s2 = "hello";

easy

A. s1 == s2

B. s1.compareTo(s2)

C. s1.equalsIgnoreCase(s2)

D. s1.equals(s2)

Solution

1. Step 1: Understand string equality in Java

   Using == compares references, not content, so it is not reliable for string content comparison.

2. Step 2: Choose the method for exact match including case

   equals() checks if two strings have exactly the same characters and case, which is what is asked.

3. Final Answer:

   s1.equals(s2) -> Option D

4. Quick Check:

   Use equals() for exact string match [OK]

Hint: Use equals() for exact string match including case [OK]

Common Mistakes:

• Using == instead of equals() for string content comparison
• Using equalsIgnoreCase() when case matters
• Using compareTo() for equality check

2. Which of the following is the correct syntax to compare two strings s1 and s2 ignoring case in Java?

easy

A. s1.compareToIgnoreCase(s2)

B. s1.equals(s2)

C. s1.equalsIgnoreCase(s2)

D. s1 == s2

Solution

1. Step 1: Identify method to compare strings ignoring case

   Java provides equalsIgnoreCase() to compare strings ignoring letter case differences.

2. Step 2: Confirm syntax correctness

   s1.equalsIgnoreCase(s2) is the correct method call syntax.

3. Final Answer:

   s1.equalsIgnoreCase(s2) -> Option C

4. Quick Check:

   Use equalsIgnoreCase() to ignore case in string comparison [OK]

Hint: Use equalsIgnoreCase() to compare strings ignoring case [OK]

Common Mistakes:

• Using equals() when ignoring case is needed
• Using == for string comparison
• Using non-existent compareToIgnoreCase() method

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

String a = "apple";
String b = "banana";
int result = a.compareTo(b);
System.out.println(result > 0 ? "a > b" : "a <= b");

medium

A. a > b

B. a <= b

C. 0

D. Compilation error

Solution

1. Step 1: Understand compareTo() behavior

   compareTo() returns a negative number if the first string is alphabetically before the second.

2. Step 2: Compare "apple" and "banana" alphabetically

   "apple" comes before "banana", so a.compareTo(b) returns a negative value, making result > 0 false.

3. Final Answer:

   a <= b -> Option B

4. Quick Check:

   compareTo() negative means first string is less [OK]

Hint: compareTo() negative means first string is alphabetically before second [OK]

Common Mistakes:

• Assuming compareTo() returns boolean
• Confusing positive and negative return values
• Expecting 0 when strings differ

4. The following code is intended to print "Strings are equal" if two strings match ignoring case. What is wrong?

String s1 = "Java";
String s2 = "java";
if (s1 == s2) {
    System.out.println("Strings are equal");
} else {
    System.out.println("Strings are not equal");
}

medium

A. Using == compares references, not content

B. Missing semicolon after if condition

C. Strings cannot be compared in Java

D. Should use compareTo() instead of ==

Solution

1. Step 1: Identify how string comparison works

   Using == compares if both variables point to the same object, not if their text is equal.

2. Step 2: Correct way to compare ignoring case

   Use s1.equalsIgnoreCase(s2) to compare string content ignoring case.

3. Final Answer:

   Using == compares references, not content -> Option A

4. Quick Check:

   Use equalsIgnoreCase() for content ignoring case [OK]

Hint: Never use == for string content comparison [OK]

Common Mistakes:

• Using == instead of equalsIgnoreCase()
• Thinking == compares string content
• Using compareTo() for equality check

5. You want to sort an array of strings alphabetically ignoring case. Which approach correctly compares two strings s1 and s2 for sorting?

hard

A. s1.compareToIgnoreCase(s2)

B. s1.equalsIgnoreCase(s2)

C. s1.compareTo(s2)

D. s1 == s2

Solution

1. Step 1: Understand sorting with string comparison

   Sorting requires a method that returns an integer indicating order, not just equality.

2. Step 2: Identify method ignoring case for order

   compareToIgnoreCase() compares strings alphabetically ignoring case and returns an int for sorting.

3. Step 3: Confirm method availability

   Java's String class has compareToIgnoreCase() for this purpose.

4. Final Answer:

   s1.compareToIgnoreCase(s2) -> Option A

5. Quick Check:

   Use compareToIgnoreCase() for case-insensitive sorting [OK]

Hint: Use compareToIgnoreCase() to sort strings ignoring case [OK]

Common Mistakes:

• Using equalsIgnoreCase() which returns boolean, not order
• Using compareTo() which is case sensitive
• Using == which compares references