AP CS Vocab 1-3

1. Machine Language

Definition: The most basic language of 0s and 1s that a computer's hardware directly understands. Watch out: Each computer model has its own unique machine language, so programs aren't portable.

2. Assembly Language

Definition: A more English-like language that uses short names instead of numbers to represent machine instructions. Example: LOAD BASEPAY is easier to read than 0101 0011.

3. Assembler

Definition: A translation program that converts assembly language instructions into machine language.

4. High-Level Language

Definition: A programming language that uses English words and familiar symbols, making it the easiest for humans to write. Example: Java and C++ are high-level languages.

5. Compiler

Definition: A translation program that converts high-level language code into the machine language of a specific computer. Watch out: This is why high-level language programs are portable across different computers.

6. Accessor Method

Definition: A method that returns the value of an instance variable without changing it. Syntax: Names usually start with "get", like getX().

7. Mutator Method

Definition: A method that changes the value of one or more instance variables. Syntax: Names usually start with "set" or an action word, like translate().

8. State of an Object

Definition: The current values of all the instance variables of an object at a given moment.

9. ASCII

Definition: A code that represents each character as a unique 8-bit pattern. Example: The letter 'A' has the ASCII value 65.

10. Unicode

Definition: A 16-bit character code that can represent 65,536 different characters, enough for most world languages. Watch out: The first 256 Unicode characters are identical to ASCII.

11. Assignment Statement

Definition: A statement that evaluates an expression and stores the result in a variable. Syntax: variable = expression; Watch out: Read the equals sign as "gets," not "equals."

12. Uninitialized Variable

Definition: A variable that has been declared but never given a value. Watch out: Using one causes a compiler error in Java.

13. Object Reference

Definition: The memory address of an object, which is what an object variable actually stores instead of the object itself. Watch out: Assigning one object variable to another copies the reference, so both variables end up pointing to the same object.

14. Garbage Collection

Definition: The automatic process Java uses to reclaim memory from objects that no variable refers to anymore.

15. this() Constructor Call

Definition: A call from one constructor to another constructor in the same class, used to avoid repeating code. Watch out: The this() call must be the very first line inside the constructor.

16. Constructor

Definition: A special method that runs automatically when an object is created, giving its instance variables initial values. Watch out: A constructor has no return type, not even void, and shares the class's exact name.

17. Default Constructor

Definition: A constructor that takes no parameters. Example: Rectangle name = new Rectangle();

18. Parameterized Constructor

Definition: A constructor that takes one or more parameters to set an object's initial values. Example: Rectangle name = new Rectangle(10,20,30,40);

19. Method Signature (Heading)

Definition: The first line of a method, listing its access specifier, return type, name, and parameter list. Example: public int getAltitude()

20. Access Specifier

Definition: A keyword that controls who is allowed to call a method, such as public.

21. return Statement

Definition: A statement that ends a method and can send a value back to whoever called it. Watch out: A void method can only use "return;" with no value after it.

22. new Operator

Definition: The Java keyword used to create a new object, calling its constructor and returning a reference to it. Example: Rectangle box = new Rectangle(10,20,30,20);

23. null

Definition: A special value meaning an object variable is not currently referring to any object. Watch out: Calling a method on a null reference throws a NullPointerException.

24. Instance Variable

Definition: A variable declared inside a class but outside any method, storing an attribute that belongs to every object of that class. Watch out: Each object created has its own separate copy of every instance variable.

25. Parameter Variable

Definition: A variable declared inside a method's heading that receives a value when the method is called.

26. Local Variable

Definition: A variable declared inside a method's body that only exists while that method is running. Watch out: It must be explicitly initialized before use, or the compiler will complain.

27. Scope (of a variable)

Definition: The portion of a program in which a variable can be accessed, or is "known."

28. Algorithm

Definition: An unambiguous, step-by-step set of instructions that is guaranteed to finish and produce a result.

29. Precondition

Definition: A requirement that must be true about an algorithm's input for it to work correctly. Watch out: If a precondition isn't met, the algorithm is allowed to fail.

30. Syntax Error

Definition: A mistake in the grammar of code that the compiler catches before the program can run. Example: Forgetting a semicolon at the end of a statement.

31. Exception (Fatal Run-Time Error)

Definition: An error that occurs while a program is executing, such as dividing by zero. Watch out: An unhandled exception makes the program crash.

32. Logic Error

Definition: A mistake where the program compiles and runs normally but produces the wrong output. Watch out: Only careful checking of the actual output can catch a logic error.

33. String

Definition: A sequence of characters, such as a word or sentence, treated as one value.

34. String Literal

Definition: Any sequence of characters enclosed in double quotes in Java code.

35. Concatenation

Definition: Joining two strings together into a single string using the plus sign. Example: "Hi" + " Mom" becomes "Hi Mom".

36. Escape Sequence

Definition: Two characters, starting with a backslash, that Java treats together as one special character. Example: \n starts a new line of output.

37. Class

Definition: The blueprint or template that defines what objects of that type know and can do. Watch out: A single class can be used to create many different objects.

38. Object

Definition: A specific instance of a class, with its own attributes (what it has) and behaviors (what it does).

39. Method

Definition: A block of code inside a class that carries out one of an object's behaviors.

40. Abstraction

Definition: Using a method by knowing only what it does, without needing to know how it works internally.

41. API (Application Programming Interface)

Definition: Documentation that lists the classes and methods available for programmers to use, along with how to call them.

42. Operator Precedence

Definition: The order in which Java performs operations when an expression has more than one operator. Watch out: Multiplication, division, and modulus happen before addition and subtraction.

43. Integer Division

Definition: Division between two integers that keeps only the whole number part of the answer and drops the remainder. Example: 9 / 5 equals 1 in Java.

44. Modulus (%)

Definition: An operator that returns the remainder left over after dividing two integers. Example: 9 % 5 equals 4.

45. main Method

Definition: The special method where every Java program begins running. Syntax: public static void main(String args[])

46. Keyword (Reserved Word)

Definition: A word with special meaning in Java that cannot be used as a name for anything else. Example: public, class, and static are keywords.

47. Identifier

Definition: A name a programmer chooses for a class, variable, or method.

48. Comment

Definition: Text in code that the compiler ignores, used to explain the program to humans. Syntax: Two forward slashes // start a single-line comment.

49. Method Overloading

Definition: Having two or more methods in the same class with the same name but different parameter lists. Watch out: Methods cannot be overloaded by return type alone.

50. Parameter vs. Argument

Definition: A parameter is the placeholder listed in a method's heading, while an argument is the actual value passed in when the method is called.

51. Encapsulation

Definition: Keeping an object's instance variables and methods bundled together and protecting the variables from being accessed directly.

52. Information Hiding

Definition: Hiding the implementation details of a class so users only need to know its methods, not how they work.

53. Reusability

Definition: The advantage of being able to use the same class to create many objects or reuse it across different programs.

54. Polymorphism

Definition: The idea that different, unrelated objects can share a similar behavior that each performs in its own way. Example: Both a bird and a plane can fly, but very differently.

55. Shadowing

Definition: When a parameter or local variable has the same name as an instance variable and blocks access to it. Watch out: Use the keyword this to reach the instance variable instead.

56. this Keyword

Definition: A reference to the current object, often used to access its instance variables when they are shadowed. Syntax: this.radius = radius;

57. toString() Method

Definition: A method that returns a String describing the current state of an object. Syntax: public String toString() Watch out: Every toString() method must use this exact signature.

58. Method Overriding

Definition: Redefining a method a class already inherited, such as toString(), to give it new behavior.

59. Variable

Definition: A named location in memory that stores one value of a specific data type.

60. Data Type

Definition: The kind of value a variable can hold, such as int, double, or String.

61. Humpback (Camel Case) Notation

Definition: A naming style where a variable starts lowercase and each following word starts with a capital letter. Example: luckyNumber and timeOfDay.