Unit 1 Day 10: String length() and indexOf() Practice

January 7, 2026

Unit 1, Section 1.10

Day 10 Practice • January 16, 2026

🎯 Focus: String Methods (length & indexOf)

Practice Question

Consider the following code segment:

String word = "Computer";
System.out.println(word.length() + word.indexOf("put"));

What is printed as a result of executing this code segment?

What This Tests: This question tests two essential String methods: length() which returns the number of characters, and indexOf() which returns the starting position of a substring.

Key Concept: String Indexing

Strings are indexed starting at 0:

//  Index:   0 1 2 3 4 5 6 7
//  String:  C o m p u t e r

"Computer".length()         // → 8 (count of characters)
"Computer".indexOf("put")   // → 4 (where "put" starts)
"Computer".indexOf("xyz")   // → -1 (not found)

Step-by-Step Trace

Expression	Explanation	Result
word.length()	"Computer" has 8 characters	8
word.indexOf("put")	"put" starts at index 4 (Computer)	4
8 + 4	Addition	12

Common Mistakes

Mistake: Answer B (11)

This comes from thinking indexOf returns where "put" ends (index 7) rather than where it starts (index 4). indexOf always returns the starting position.

Mistake: Answer D (13)

This might come from counting "put" as starting at position 5 (counting from 1 instead of 0). Remember: Java strings are 0-indexed!

String Methods Reference

💡 Essential String Methods for AP CSA

length() - Returns number of characters

indexOf(str) - Returns index where str starts (-1 if not found)

substring(start) - Returns from start to end

substring(start, end) - Returns from start to end-1

equals(str) - Compares content (case-sensitive)

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