1) Assignment Statements
An assignment statement stores a value into a variable using the assignment operator
=. It means “evaluate the expression on the right, then store the result into the variable on the left.”
Example
int score = 10; // declare and initialize
score = score + 5; // update: score becomes 15
• The variable on the left must already exist and have a compatible type.
•
= is assignment; == is comparison.• You cannot assign to a literal (e.g.,
5 = score; is invalid).
Right-to-Left Evaluation
Java evaluates the right-hand side first, then assigns the result:
x = y + 3; // 1) read y 2) compute y + 3 3) store into x
2) Getting Input with Scanner
In APCSA, user input commonly uses the Scanner class from java.util.
Create a scanner that reads from the keyboard (standard input).
import java.util.Scanner;
public class InputDemo {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("Enter your age: ");
int age = input.nextInt(); // assignment from input
System.out.print("Enter your name: ");
String name = input.next(); // reads a single word
System.out.println("Hello, " + name + ". You are " + age + " years old.");
input.close();
}
}
Common Scanner Methods
| Method | Purpose | Example Input |
|---|---|---|
nextInt() |
Read an integer. | 17 |
nextDouble() |
Read a decimal (double). | 3.14 |
next() |
Read one word (stops at space). | Cusack |
nextLine() |
Read an entire line (can include spaces). | Joe Cusack |
nextInt() or nextDouble(),
call input.nextLine() once to consume the leftover newline before using nextLine() for text.
3) Assignment + Input Together
Assignments often store values directly from user input and then use those values in expressions.
import java.util.Scanner;
public class DoubleNumber {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("Enter a number: ");
int num = input.nextInt(); // assignment from input
int doubleNum = num * 2; // computed assignment
System.out.println("Twice your number is " + doubleNum);
input.close();
}
}
4) APCSA Relevance
College Board AP CSA Unit 1 (Primitive Types) expects you to declare variables, assign and reassign values, read input, and print results. Mastering assignment and input prepares you for later units on expressions, methods, and objects—nearly all data handling begins here.