Unit 1 · Using Objects and Methods
String Immutability
Practice mode with 15 Java-focused questions, immediate answer checks, and explanations.
What string immutability covers
Strings in Java cannot be modified in place. Methods such as substring, toUpperCase, and replace return a brand-new String and leave the original untouched. A variable only changes when you assign the result back to it. Comparison follows the same object logic: equals compares character content, while == compares references and can be false for two Strings with identical text.
Where students lose points
Calling s.toUpperCase(); without assigning the result and then expecting s to have changed is the defining error of this topic. Students also use == to compare String content, which may appear to work for literals because of interning and then fail for Strings built at runtime.
How it shows up on the AP exam
Unit 1 content with consequences across the whole exam. Immutability explains why String parameters cannot be changed by a method, which is a recurring MCQ theme and a frequent source of lost FRQ points.
For practice use only.
String Immutability MCQ Practice
AP CSA String immutability practice: why String methods return new values, when concatenation actually changes a variable, and how == differs from equals.
Answered 0 of 15
Choose one answer.
Which option matches the complete output produced by this segment?
public class StringImmutabilityContext
{
public static void runExample()
{
String s = "cat";
s.substring(0, 2);
System.out.print(s);
}
public static void main(String[] args)
{
runExample();
}
}