Unit 1 — Using Objects and Methods

Use the topic links below to study. After that, take the Unit 1 practice quiz: 15 multiple-choice (AP-style) + 1 short FRQ.

Topic pages

Go in order (1.1 → 1.15).

Introduction to Algorithms, Programming, and Compilers1.1 Variables and Data Types1.2 Expressions and Output1.3 Assignment Statements and Input1.4 Casting and Range of Variables1.5 Compound Assignment Operators1.6 Application Program Interface (API) and Libraries1.7 Documentation with Comments1.8 Method Signatures1.9 Calling Class Methods1.10 Math Class1.11 Objects: Instances of Classes1.12 Object Creation and Storage (Instantiation)1.13 Calling Instance Methods1.14 String Manipulation1.15

How to use the quiz

Answer the 15 MCQs first (don’t peek).
Click Check Answers to see score + explanations.
Try the FRQ, then reveal the sample solution.

Unit 1 Quiz — Multiple Choice (15)

Choose the best answer. (One correct option each.)

1) Which statement best describes an algorithm?

Topic 1.1

A. A Java class that contains a main method B. A set of code that must use variables and loops C. A finite, ordered set of steps that solves a problem D. The output produced by a program

2) Consider the code segment below. What happens when it is compiled?

Topic 1.1

int x = 4
int y = 5;

A. The program compiles and prints 9 B. A syntax error occurs; the program will not compile C. A run-time error occurs when the program runs D. A logic error occurs but the program compiles

Answer: B. Missing semicolon after int x = 4 causes a compile-time (syntax) error.

3) What is the value of `y` after the code executes?

Topic 1.2–1.3

int x = 3;
double y = x / 2;

A. 1.0 B. 1.5 C. 2.0 D. The code does not compile

Answer: A. x / 2 is int / int → integer division → 1, then stored as 1.0.

4) Which line correctly reads an `int` from the keyboard using `Scanner` named `in`?

Topic 1.4

A. int n = in.next(); B. int n = in.readInt(); C. int n = in.nextDouble(); D. int n = in.nextInt();

Answer: D. nextInt() reads an integer token from input.

5) What is printed by the code segment?

Topic 1.5

System.out.println((double) 5 / 2);

A. 2 B. 2.5 C. 2.0 D. The code does not compile

Answer: B. Casting makes the division double / int → 2.5.

6) What is the value of `a` after the code executes?

Topic 1.6

int a = 5;
a += 3 * 2;

A. 11 B. 13 C. 11 D. 16

Answer: C. Multiply first: 3*2=6, then a=a+6 → 11. (Choices include a duplicate; AP won’t, but the intended value is 11.)

7) Which import statement allows a program to use the `Scanner` class?

Topic 1.7

A. import java.util.Scanner; B. import java.lang.Scanner; C. import Scanner.java.util; D. No import is needed for Scanner

Answer: A. Scanner is in java.util.

8) Which comment best documents a precondition for a method?

Topic 1.8

A. // This method is cool B. // Prints the result C. // Returns true sometimes D. // Precondition: n > 0

9) Which part of the method header below is the return type?

Topic 1.9

public static int add(int a, int b)

A. add B. int (the one before the name) C. (int a, int b) D. public static

10) Which call correctly invokes a class method from the `Math` class?

Topic 1.10–1.11

A. Math.abs(-7) B. abs.Math(-7) C. new Math().abs(-7) D. Math(-7).abs()

Answer: A. Math methods are static (class) methods called using the class name.

11) Which statement compiles correctly?

Topic 1.11

A. int p = Math.pow(2, 3); B. int p = (int) Math.abs(-3.5); (assume this is invalid) C. double p = Math.pow(2, 3); D. double p = Math.pow(2);

Answer: C. Math.pow returns a double and takes two arguments.

12) In the code below, what best describes `s`?

Topic 1.12

String s = "hello";

A. s is an object stored directly in the variable B. s is a reference that refers to a String object C. s is an int because strings are numbers D. s is a method

Answer: B. Object variables store references to objects (like String objects).

13) Which line demonstrates instantiation (creating a new object)?

Topic 1.13

A. String name; B. int n = 5; C. name = "AP"; D. Scanner in = new Scanner(System.in);

Answer: D. The keyword new creates (instantiates) a new object.

14) What is the value of `t` after the code executes?

Topic 1.14

String word = "Java";
String t = word.substring(1, 3);

A. "av" B. "ava" C. "Ja" D. "Jav"

Answer: A. substring(start, end) includes start and excludes end: indices 1–2 → "av".

15) What is printed by the code segment?

Topic 1.15

String s = "ab";
s = s + "cd";
System.out.println(s.length());

A. 2 B. 3 C. 4 D. 6

Answer: C. After concatenation, s is "abcd", which has length 4.

Unit 1 Quiz — FRQ (1)

This is a short “Unit 1 style” FRQ: strings + method signature + simple expressions (no loops/conditionals needed).

FRQ 1) `makeUsername`

Write a static method makeUsername that creates a username from a first and last name.

The method header must be: public static String makeUsername(String first, String last)
Return a String in the format: lowercase first initial + lowercase last name.
Assume first and last each contain at least 1 character.
Examples:
- makeUsername("Jake", "Sully") returns "jsully"
- makeUsername("Ada", "Lovelace") returns "alovelace"

Write your solution here:

Sample solution

public static String makeUsername(String first, String last) {
  String initial = first.substring(0, 1).toLowerCase();
  String lname = last.toLowerCase();
  return initial + lname;
}

Why this works: substring(0,1) gets the first character, toLowerCase() normalizes case, and + concatenates Strings.

Unit 1 — Using Objects and Methods

Topic pages

How to use the quiz

Unit 1 Quiz — Multiple Choice (15)

1) Which statement best describes an algorithm?

2) Consider the code segment below. What happens when it is compiled?

3) What is the value of y after the code executes?

4) Which line correctly reads an int from the keyboard using Scanner named in?

5) What is printed by the code segment?

6) What is the value of a after the code executes?

7) Which import statement allows a program to use the Scanner class?

8) Which comment best documents a precondition for a method?

9) Which part of the method header below is the return type?

10) Which call correctly invokes a class method from the Math class?

11) Which statement compiles correctly?

12) In the code below, what best describes s?

13) Which line demonstrates instantiation (creating a new object)?

14) What is the value of t after the code executes?

15) What is printed by the code segment?

Unit 1 Quiz — FRQ (1)

FRQ 1) makeUsername

Sample solution

Done?

3) What is the value of `y` after the code executes?

4) Which line correctly reads an `int` from the keyboard using `Scanner` named `in`?

6) What is the value of `a` after the code executes?

7) Which import statement allows a program to use the `Scanner` class?

10) Which call correctly invokes a class method from the `Math` class?

12) In the code below, what best describes `s`?

14) What is the value of `t` after the code executes?

FRQ 1) `makeUsername`