Rucete ✏ AP Computer Science A In a Nutshell
1. Introductory Java Language Features
This chapter introduces basic Java programming concepts, including packages and classes, types and identifiers, operators, input/output, control structures, and handling errors and exceptions.
Packages and Classes
• Related classes are grouped into packages (e.g., java.util, java.lang).
• The java.lang package is automatically imported; others require explicit import statements.
• A Java program must have at least one class containing the main method.
• Source code is compiled into bytecode for execution.
Identifiers
• Identifiers name variables, methods, classes, etc., and are case-sensitive.
• Naming conventions: variables/methods start with lowercase, classes start with uppercase letters.
• Reserved words (e.g., public, static) cannot be used as identifiers.
Built-in Types
• int: 32-bit signed integers, bounded by Integer.MIN_VALUE and Integer.MAX_VALUE.
• double: 64-bit floating-point numbers, subject to roundoff error.
• Type casting is needed when converting between incompatible types (e.g., double to int truncates).
Final Variables (Constants)
• Declared using the keyword final and typically named in all capitals.
• Example: final int DAYS_IN_WEEK = 7;
Storage of Numbers
• Integers are stored exactly; doubles use scientific notation with potential roundoff error.
• Floating-point results like NaN or Infinity occur during undefined operations or division by zero.
Hexadecimal and Octal Numbers
• Not part of the AP Java subset; only base-10 numbers are used.
Operators
• Arithmetic Operators: +, -, *, /, %, ++, --.
• Division between integers discards the fractional part (e.g., 5/2 = 2).
• Modulus (%) returns the remainder after integer division.
Relational Operators
• Compare two values: ==, !=, <, >, ≤, ≥.
• Used to create Boolean expressions for control structures.
Logical Operators
• AND (&&): True only if both operands are true.
• OR (||): True if at least one operand is true.
• NOT (!): Reverses the truth value.
Assignment Operators
• Basic assignment: =.
• Shorthand operators: +=, -=, *=, /=, %=.
• Example: x += 5; is the same as x = x + 5;
System Output
• System.out.print(): Prints output without moving to the next line.
• System.out.println(): Prints output and moves to the next line.
Escape Sequences
• \\n: New line.
• \\t: Tab.
• \\\": Double quote inside a string.
• \\\\: Backslash inside a string.
Control Structures: if Statements
• Simple if: Executes code block if a condition is true.
• if-else: Chooses between two code blocks based on a condition.
• Nested ifs: if-else within another if-else for multiple conditions.
Switch Statements
• Switch selects among many alternatives based on a single variable’s value.
• break statements prevent fall-through to other cases.
• default handles unmatched cases.
Loops
• while loop: Repeats while a condition is true; condition is checked before each iteration.
• for loop: Compact loop with initialization, condition check, and update in a single line.
• Example: for (int i = 0; i < 10; i++) { }
Common Loop Pitfalls
• Infinite loops occur when the condition never becomes false.
• Off-by-one errors happen when the loop runs one too many or one too few times.
Errors and Exceptions
• Compile-time errors: Detected by the compiler before running the program (e.g., syntax errors).
• Run-time errors: Occur while the program is running (e.g., division by zero).
• Logic errors: Program runs but produces incorrect results due to flaws in reasoning.
Handling Errors
• Java uses try-catch blocks to handle exceptions.
• try block contains code that might throw an exception; catch block handles it gracefully.
In a Nutshell
Mastering introductory Java features—including types, operators, input/output, control structures, and error handling—lays the foundation for building robust and efficient programs. Clear understanding of syntax rules, proper use of loops and conditionals, and effective debugging practices are critical skills for success in Java programming.