String creation in Java - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the simplest way to create a String in Java?

You can create a String by enclosing text in double quotes, like String s = "Hello";. This is called a string literal.

intermediate

What does new String("text") do compared to a string literal?

It creates a new String object in memory, even if the same text exists as a literal. This is less efficient than using literals directly.

beginner

Can Strings in Java be changed after creation?

No, Strings are immutable. Once created, their content cannot be changed. Any modification creates a new String object.

intermediate

How does Java optimize String creation with literals?

Java uses a String pool to store literals. If a literal already exists, Java reuses it instead of creating a new object.

intermediate

What is the difference between String s = "abc"; and String s = new String("abc");?

The first uses the String pool and reuses the literal if available. The second always creates a new String object in memory.

Which of these creates a String literal in Java?

A String s = StringBuilder.append("Hello");

B String s = new String("Hello");

C char[] s = {'H','e','l','l','o'};

D String s = "Hello";

String literals are created by enclosing text in double quotes directly, like String s = "Hello";.

What happens when you create a String with new String("abc")?

A It creates a new String object in memory.

B It creates a StringBuilder object.

C It reuses an existing String from the pool.

D It throws an error.

Using new String() always creates a new String object, even if the same text exists in the pool.

Are Java Strings mutable (can they be changed after creation)?

A No, Strings are immutable.

B Yes, you can change characters inside a String.

C Only if you use StringBuilder.

D Only if you use new String().

Java Strings are immutable, meaning their content cannot be changed after creation.

What is the purpose of the String pool in Java?

A To store all String objects created with new.

B To store unique String literals for reuse.

C To speed up String concatenation.

D To convert Strings to char arrays.

The String pool stores unique String literals so Java can reuse them and save memory.

Which is more memory efficient for creating Strings?

A Using char arrays

B Using new String("text")

C Using String literals like "text"

D Using StringBuilder

String literals are stored in the pool and reused, making them more memory efficient than creating new String objects.

Explain how Java creates and stores Strings using literals and the new keyword.

Think about how Java reuses text in memory.

Why are Java Strings immutable and what does that mean for modifying text?

Consider what happens if you try to change a String's characters.

Practice

1. Which of the following is the correct way to create a string variable in Java?

easy

A. String greeting = "Hello";

B. string greeting = 'Hello';

C. String greeting = Hello;

D. String greeting = "Hello"

Solution

1. Step 1: Check the data type and quotes

   Java strings use the class String with a capital S and text must be in double quotes.

2. Step 2: Validate syntax correctness

   String greeting = "Hello"; uses correct capitalization, double quotes, and ends with a semicolon.

3. Final Answer:

   String greeting = "Hello"; -> Option A

4. Quick Check:

   String creation uses String and double quotes [OK]

Hint: Use capital S in String and double quotes for text [OK]

Common Mistakes:

• Using single quotes instead of double quotes
• Using lowercase 'string' instead of 'String'
• Missing semicolon at the end

2. Which of the following lines will cause a syntax error in Java?

easy

A. String name = "Alice";

B. String name = 'Alice';

C. String name = "Bob";

D. String name = "Charlie";

Solution

1. Step 1: Identify correct string literal syntax

   Java strings must be enclosed in double quotes, not single quotes.

2. Step 2: Check each option

   String name = 'Alice'; uses single quotes which is invalid for strings in Java, causing a syntax error.

3. Final Answer:

   String name = 'Alice'; -> Option B

4. Quick Check:

   Strings need double quotes, single quotes cause syntax error [OK]

Hint: Remember: Java strings use double quotes only [OK]

Common Mistakes:

• Using single quotes for strings
• Confusing char literals with strings
• Missing semicolon

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

String first = "Good";
String second = "Morning";
System.out.println(first + " " + second);

medium

A. GoodMorning

B. Good+Morning

C. Good Morning

D. gninroM dooG

Solution

1. Step 1: Understand string concatenation

   The + operator joins strings. Here, first + " " + second adds a space between words.

2. Step 2: Combine the strings

   "Good" + " " + "Morning" results in "Good Morning" with a space.

3. Final Answer:

   Good Morning -> Option C

4. Quick Check:

   + joins strings including spaces [OK]

Hint: Use + with " " to add spaces between words [OK]

Common Mistakes:

• Forgetting to add space between words
• Using + without quotes for space
• Expecting + to print plus sign

4. Find the error in the following code snippet:

String text = "Hello"
System.out.println(text);

medium

A. System.out.println syntax is wrong

B. Incorrect string quotes

C. Variable name is invalid

D. Missing semicolon after string assignment

Solution

1. Step 1: Check string assignment line

   The line ends without a semicolon, which is required in Java statements.

2. Step 2: Verify other lines

   Quotes are correct, variable name is valid, and print statement syntax is correct.

3. Final Answer:

   Missing semicolon after string assignment -> Option D

4. Quick Check:

   Every statement must end with a semicolon [OK]

Hint: Always end Java statements with a semicolon [OK]

Common Mistakes:

• Omitting semicolon at end of statement
• Confusing quotes with apostrophes
• Misnaming variables

5. You want to create a string variable that holds the full name by combining first and last names with a space. Which code correctly does this?

hard

A. String fullName = firstName + " " + lastName;

B. String fullName = firstName + lastName;

C. String fullName = firstName.concat(lastName);

D. String fullName = firstName - lastName;

Solution

1. Step 1: Understand string concatenation with space

   To add a space between first and last names, include " " between them.

2. Step 2: Check each option

   String fullName = firstName + " " + lastName; correctly uses + operator with a space string. String fullName = firstName + lastName; misses space, C concatenates without space, D uses invalid operator.

3. Final Answer:

   String fullName = firstName + " " + lastName; -> Option A

4. Quick Check:

   Use + " " + to add space between strings [OK]

Hint: Add " " between strings to insert space [OK]

Common Mistakes:

• Forgetting space between names
• Using invalid operators like -
• Using concat() without space