AP Computer Science A: Input/Output quiz (Scanner & System.out.println())

📚 Quick Study Guide: AP CS A Input/Output Essentials

• 🔍 Scanner Class: The primary tool in Java for reading input from various sources, most commonly the keyboard (`System.in`).
• ✍️ Import Statement: To use `Scanner`, you must include `import java.util.Scanner;` at the top of your Java file.
• 🛠️ Object Creation: Instantiate a `Scanner` object like this: `Scanner console = new Scanner(System.in);`.
• 🔢 Reading Data Types:
  • `nextInt()`: Reads an integer value.
  • `nextDouble()`: Reads a double-precision floating-point value.
  • `next()`: Reads a single token (word) delimited by whitespace.
  • `nextLine()`: Reads the entire line of text until the end-of-line character.
• ⚠️ Newline Consumption: After using `nextInt()`, `nextDouble()`, or `next()`, a newline character often remains in the input buffer. Calling `nextLine()` immediately after these without an intermediate `nextLine()` can lead to unexpected empty string reads.
• ♻️ Closing Scanner: It's good practice to close the `Scanner` object when no longer needed to release system resources: `console.close();`.
• 🗣️ System.out.println(): Prints the argument to the console and then advances the cursor to the next line.
• ➡️ System.out.print(): Prints the argument to the console without advancing the cursor to the next line.
• ➕ String Concatenation: Use the `+` operator to combine strings with variables or other data types for output (e.g., `"Hello " + name`).
• 📝 Escape Sequences: Special character combinations within strings:
  • `\n`: Newline
  • `\t`: Tab
  • `\"`: Double quote
  • `\\`: Backslash

🧠 Practice Quiz: Test Your I/O Knowledge!

1. Which `Scanner` method is used to read an entire line of text, including spaces, until a newline character is encountered?

• A) `next()`
• B) `nextInt()`
• C) `nextLine()`
• D) `nextWord()`

2. What is the correct way to import the `Scanner` class in Java?

• A) `import java.io.Scanner;`
• B) `import java.util.Scanner;`
• C) `import java.lang.Scanner;`
• D) `import Scanner.java.util;`

3. Consider the following code:

Scanner input = new Scanner(System.in);
System.out.print("Enter your age: ");
int age = input.nextInt();
System.out.println("You are " + age + " years old.");
input.close();

If the user types `20` and presses Enter, what will be the exact output?

• A) Enter your age: 20You are 20 years old.
• B) Enter your age: 20
You are 20 years old.
• C) Enter your age: You are 20 years old.
• D) Enter your age:
20
You are 20 years old.

4. Which of the following statements correctly creates a `Scanner` object to read input from the keyboard?

• A) `Scanner keyboard = new Scanner();`
• B) `Scanner keyboard = new Scanner(System.out);`
• C) `Scanner keyboard = new Scanner(System.in);`
• D) `Scanner keyboard = new System.in.Scanner();`

5. What is the primary difference between `System.out.print()` and `System.out.println()`?

• A) `print()` outputs to a file, `println()` outputs to the console.
• B) `print()` adds a newline character at the end, `println()` does not.
• C) `println()` adds a newline character at the end, `print()` does not.
• D) `print()` is for strings, `println()` is for numbers.

6. Which escape sequence represents a tab character in a Java string literal?

• A) `\n`
• B) `\r`
• C) `\"`
• D) `\t`

7. What happens if you try to call `input.nextLine()` immediately after `input.nextInt()` without consuming the newline character?

• A) It will correctly read the next line of user input.
• B) It will throw an `InputMismatchException`.
• C) It will read the leftover newline character from the `nextInt()` input, resulting in an empty string.
• D) It will wait indefinitely for new input.