1.3: Expressions and Assignment Statements

Now, we can start working more with these data types. In this section, we're going to focus on the two numeric types: int and double.

For addition, subtraction, and multiplication, equations can be input as you would input them into your calculator. Variables are used to assign the answers to the correct equation.

int a = 1 + 2;
double b = 1.0 + 3.5;
int c = 3 - 5;
double d = 24 * 1.0


, can be used to change the value of the variable or other expressions. It evaluates the expression first and stores the final value in the variable.

If an operation has two integers, then the result is an integer. If an operation has at least one double, then the result is a double.

There is also a 

, the program reports the integer remainder of 

 is positive. We will only talk about modulo with positive values of 

 because once a is negative, the math becomes much more complicated. A few examples are below:

int a = 4 % 2;
int b = 10 % 3;
int c = 3 % 5;



a = 0 (4 = 2 * 2 + **0**)
b = 1 (10 = 3 * 3 + **1**)
c = 3 (3 = 0 * 5 + **3**)


Things get a bit more complicated with division. Remember that operations with two integers return an integer, and if there is at least one double, it returns a double. Here is an example of each:

 returns only the whole number quotient, while the 

 returns the actual quotient as a decimal.

Java follows the regular order of operations that you learned in algebra, with the inclusion of modulo with multiplication and division. Here is a table of the order of operations with operators from highest to lowest precedence:


Here is some practice with order of operations. Remember the difference between double division and integer division. Find the value of each variable in the following:

int a = 3 + 4 / 3 * (4-1);
double b = (3 * 5 / 2) / (2.0 + 8);
int c = 4 % 3 + 2 * 5 / 4; 
int d = (3 * 5 / 2) / (2 + 8);


a = 3 + 4 / 3 * (4 - 1) = 3 + 4 / 3 * 3 = 3 + 1 * 3 = 3 + 3 = **6**
b = (3 * 5 / 2) / (2.0 + 8) = (15 / 2) / (10.0) = (7) / (10.0) = **0.7**
c = 4 % 3 + 2 * 5 / 4 = 1 + 2 * 5 / 4 = 1 + 10 / 4 = 1 + 2 = **3**
d = (3 * 5 / 2) / (2 + 8) = (15 / 2) / (10) = (7) / (10) = **0**


AP Computer Science A

AP Computer Science A unit 1 covers primitive types, variables, data types, expressions, assignments and so much more to prepare you for your exam and make sure you understand everything in unit 1.

Unit 1 – Primitive Types

To help you understand unit 2 of AP Computer Science A take a look at all of our resources. We cover using objects, void methods, non-void methods, string objects, string methods, and so much more! With helpful examples and study guides you will understand unit 2 in no time!

Unit 2 – Using Objects

Take a look at these resources on AP Computer Science A unit 3 to help you prepare. We cover boolean expressions with examples of compound, equivalent, and complex boolean expressions, along with if-statements, else-if statements and comparing objects. All of these resources will make sure you have a better understanding of unit 3.

Unit 3 – Boolean Expressions & if Statements

Learn everything you need to know about AP Computer Science A unit 4 using these resources. We cover the role of iteration, along with nested iteration and code analysis. There are also resources explaining, with examples, while loops and for loops to ensure you know everything about unit 4!

Unit 4 – Iteration

These resources will make sure you understand AP Computer Science A unit 5. Study guides, explanations and examples are available for all the important topics including constructors, the mutator method, writing methods, accessor methods, along with so much more. 

Unit 5 – Writing Classes

Resources to help you review and understand unit 6 of AP Computer Science A. We cover arrays, with an overview, how to create them, and more, as well as detailed descriptions and examples for traversing arrays, array loops, and algorithms for arrays. 

Unit 6 – Array

Take a look at all of these resources for unit 7 of Computer Science A. They cover an introduction into an arraylist, along with helpful examples and explanations for methods, traversing arraylists, sorting arraylists, and the ethical dilemmas of data collection, along with so much more. These resources will make sure you understand unit 7!

Unit 7 – ArrayList

Make sure to check ou these resources for AP Computer Science A unit 8. We provide helpful resources and examples so you can gain a better understanding of 2D arrays and traversing 2D arrays, along with other important topics. These resources will make sure you fully understanding unit 8 of AP Computer Science A!

Unit 8 – 2D Array 

A complete overview of the important topics for unit 9 of AP Computer Science A. We cover inheritance, constructors with subclasses, super keyword, polymorphism, and object superclasses to help you study and prepare. 

Unit 9 – Inheritance

Learn everything you need to know about unit 10 of AP Computer Science A. We cover recursion and how to use recursion with sorting and searching, including linear and sequential searches, binary searches, insertion sorts, selection sorts and merge sorts. These examples and explanations will make sure you understand this final unit!

Unit 10 – Recursion

Frequently Asked Questions

Exam Reviews

Check out these resources that will cover all the important topics of AP Computer Science A so you can prepare for your exam. With study guides, review sheets and review videos with sample problems and helpful tips, these resources will make sure you are ready for your exam!

Big Reviews: Finals & Exam Prep

AP Cram Sessions 2021

First Unit

Overview

1.1 Why Programming? Why Java?

1.2 Variables and Primitive Data Types

Input

1.3 Expressions and Assignment Statements

1.4 Compound Assignment Operators

1.5 Casting and Ranges of Variables

Unit 1 Overview: Primitive Types

Why Programming? Why Java?

Intro to Programming

The Anatomy of a Java Program

System.out.println() vs System.out.print()

Variables and Data Types

Primitive Data Types

Variables

Input Using the Scanner Class

Variables and Primitive Data Types

Expressions and Assignment Statements

Basic Math in Java

Order of Operations in Java

Basic Math Practice Problems in Java

Compound Assignment Operators

Compound Operators

Incrementing and Decrementing

Code Tracing Practice

Casting

Integers to Doubles

Doubles to Integers

Rounding

Casting and Ranges of Variables

Multiple Choice Practice for Primitive Types

Multiple Choice Questions

Answers and Review for Multiple Choice Practice on Primitive Types

MC Answers and Review


The Big Takeaway Of This Unit

Unit Overview

Exam Weighting

Enduring Understanding

Building Computational Thinking

Main Ideas for This Unit

2.1: Objects: Instances of Classes


2.2 Creating and Storing Objects (Initialization)

2.3 Calling a Void Method

2.4 Calling a Void Method with Parameters


2.5 Calling a Non-Void Method


2.6 String Objects: Concatenation, Literals, and More


2.7 String Methods


2.8 Using the Math Class

Using Objects Overview

What are Objects?

What is a Class?

Objects are Instances of Classes

Real-world Example

Objects: Instances of Classes

Multiple Choice Practice for Using Objects

Answers and Review for Multiple Choice Practice on Using Objects

Constructors and Initialization

Constructor Overloading

Null Objects

Creating and Storing Objects (Instantiation)

Introduction to Methods

Void Methods vs. Non-Void Methods

Static vs. Non-Static Methods

Methods Practice Problems

Calling a Void Method

How To Write and Call Methods With Parameters

Overloading Methods

Calling a Void Method With Parameters

Returning Integers/Doubles

Returning Booleans

Returning Strings

Returning Objects and Other Reference Types

Non-Void Methods Practice Problems

Calling a Non-Void Method

A Technical Look At Strings

Escape Characters

String Concatenation

String Concatenation Practice Problems

Summary of String Objects

String Objects: Concatenation, Literals, and More

Intro to External Libraries and APIs

About the String Class

String Methods: Accessing Substrings

String Methods: Equality and Comparison

AP CS A Java Quick Reference Sheet

String Method Practice Problems

indexOf Practice Problems

Length Practice Problems

Substring Practice Problems

compareTo Practice Problems

String Methods

Introduction

Integer Wrapper Class

Double Wrapper Classes

Autoboxing

Practice Problems

Wrapper Classes: Integer and Double

Absolute Values

Exponents and Square Roots

Random Numbers

Using the Math Class

The Big Takeaway Of This Unit


Unit Overview


Building Computational Thinking

Potential Unit 3 Topics

Unit 3 Key Concepts

Unit 3 Overview: Boolean Expressions and if Statements

Boolean Operators

Boolean Expressions

Introduction to Conditional Statements

If Statements

Example: Even Number Checker

If Statements and Control Flow

If-Else Statements

Example: Number Rounding

Else If Statements

Example: Divisibility Counter

Example: Leap Year Decider

Nested Conditionals

Boolean Logical Operators

Compound Conditional Statements

Compound Boolean Expressions

Proof By Simplification

Basic Theorems


Consensus Theorems (Nice to know, but not required)

Commutative Law (boolean AND and OR are commutative)

Associative Law (boolean AND and OR are associative)

Distributive Law (boolean AND distributes over boolean OR)

DeMorgan's Theorems (Important to know) (boolean NOT does not distribute over boolean OR or AND)

Proof By Testing All Cases

Truth Table Example 1

Truth Table Example 2

Equivalent Boolean Expressions

What it Means When Objects Are Equal

The Equals Method

Comparing Objects

Multiple Choice Practice for Boolean Expressions and if Statements

Answers and Review for Multiple Choice Practice on Boolean Expressions and if Statements

1.3 Expressions and Assignment Statements

AP Computer Science A 💻

1.3: Expressions and Assignment Statements

Basic Math in Java

Order of Operations in Java

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