Using Objects and Methods · ⁨استخدام الأدوات والأساليب⁩

Learning Objective 1.1.A: Represent patterns and algorithms found in everyday life using written language or diagrams.

• 1.1.A.1 Algorithms define step-by-step processes to follow when completing a task or solving a problem. These algorithms can be represented using written language or diagrams.
• 1.1.A.2 Sequencing defines an order for when steps in a process are completed. Steps in a process are completed one at a time.

Learning Objective 1.1.B: Explain the code compilation and execution process.

• 1.1.B.1 Code can be written in any text editor; however, an integrated development environment (IDE) is often used to write programs because it provides tools for a programmer to write, compile, and run code.
• 1.1.B.2 A compiler checks code for some errors. Errors detectable by the compiler need to be fixed before the program can be run.

Learning Objective 1.1.C: Identify types of programming errors.

• 1.1.C.1 A syntax error is a mistake in the program where the rules of the programming language are not followed. These errors are detected by the compiler.
• 1.1.C.2 A logic error is a mistake in the algorithm or program that causes it to behave incorrectly or unexpectedly. These errors are detected by testing the program with specific data to see if it produces the expected outcome.
• 1.1.C.3 A run-time error is a mistake in the program that occurs during the execution of a program. Run-time errors typically cause the program to terminate abnormally.
• 1.1.C.4 An exception is a type of run-time error that occurs as a result of an unexpected error that was not detected by the compiler. It interrupts the normal flow of the program's execution.

Learning Objective 1.2.A: Identify the most appropriate data type category for a particular specification.

• 1.2.A.1 A data type is a set of values and a corresponding set of operations on those values. Data types can be categorized as either primitive or reference.
• 1.2.A.2 The primitive data types used in this course define the set of values and corresponding operations on those values for numbers and Boolean values.
• 1.2.A.3 A reference type is used to define objects that are not primitive types.

Learning Objective 1.2.B: Develop code to declare variables to store numbers and Boolean values.

• 1.2.B.1 The three primitive data types used in this course are int, double, and boolean. An int value is an integer. A double value is a real number. A boolean value is either true or false.
  • Exclusion statement: The other five primitive data types (long, short, byte, float, and char) are outside the scope of the AP Computer Science A course and exam.
• 1.2.B.2 A variable is a storage location that holds a value, which can change while the program is running. Every variable has a name and an associated data type. A variable of a primitive type holds a primitive value from that type.

Learning Objective 1.3.A: Develop code to generate output and determine the result that would be displayed.

• 1.3.A.1 System.out.print and System.out.println display information on the computer display. System.out.println moves the cursor to a new line after the information has been displayed, while System.out.print does not.

Learning Objective 1.3.B: Develop code to utilize string literals and determine the result of using string literals.

• 1.3.B.1 A literal is the code representation of a fixed value.
• 1.3.B.2 A string literal is a sequence of characters enclosed in double quotes.
• 1.3.B.3 Escape sequences are special sequences of characters that can be included in a string. They start with a \ and have a special meaning in Java. Escape sequences used in this course include double quote \", backslash \\, and newline \n.

Learning Objective 1.3.C: Develop code for arithmetic expressions and determine the result of these expressions.

• 1.3.C.1 Arithmetic expressions, which consist of numeric values, variables, and operators, include expressions of type int and double.
• 1.3.C.2 The arithmetic operators consist of addition +, subtraction -, multiplication *, division /, and remainder %. An arithmetic operation that uses two int values will evaluate to an int value. An arithmetic operation that uses at least one double value will evaluate to a double value.
  • Exclusion statement: Expressions that result in special double values (e.g., infinities and NaN) are outside the scope of the AP Computer Science A course and exam.
• 1.3.C.3 When dividing numeric values that are both int values, the result is only the integer portion of the quotient. When dividing numeric values that use at least one double value, the result is the quotient.
• 1.3.C.4 The remainder operator % is used to compute the remainder when one number a is divided by another number b.
  • Exclusion statement: The use of values less than 0 for a and the use of values less than or equal to 0 for b is outside the scope of the AP Computer Science A course and exam.
• 1.3.C.5 Operators can be used to construct compound expressions. At compile time, numeric values are associated with operators according to operator precedence to determine how they are grouped. Parentheses can be used to modify operator precedence. Multiplication, division, and remainder have precedence over addition and subtraction. Operators with the same precedence are evaluated from left to right.
• 1.3.C.6 An attempt to divide an integer by the integer zero will result in an ArithmeticException.
  • Exclusion statement: The use of dividing by zero when one numeric value is a double is outside the scope of the AP Computer Science A course and exam.

Learning Objective 1.4.A: Develop code for assignment statements with expressions and determine the value that is stored in the variable as a result of these statements.

• 1.4.A.1 Every variable must be assigned a value before it can be used in an expression. That value must be from a compatible data type. A variable is initialized the first time it is assigned a value. Reference types can be assigned a new object or null if there is no object. The literal null is a special value used to indicate that a reference is not associated with any object.
• 1.4.A.2 The assignment operator = allows a program to initialize or change the value stored in a variable. The value of the expression on the right is stored in the variable on the left.
  • Exclusion statement: The use of assignment operators inside expressions (e.g., a = b = 4; or a[i += 5]) is outside the scope of the AP Computer Science A course and exam.
• 1.4.A.3 During execution, an expression is evaluated to produce a single value. The value of an expression has a type based on the evaluation of the expression.

Learning Objective 1.4.B: Develop code to read input.

• 1.4.B.1 Input can come in a variety of forms, such as tactile, audio, visual, or text. The Scanner class is one way to obtain text input from the keyboard.
  • Exclusion statement: Any specific form of input from the user is outside the scope of the AP Computer Science A course and exam.

Learning Objective 1.5.A: Develop code to cast primitive values to different primitive types in arithmetic expressions and determine the value that is produced as a result.

• 1.5.A.1 The casting operators (int) and (double) can be used to convert from a double value to an int value (or vice versa).
• 1.5.A.2 Casting a double value to an int value causes the digits to the right of the decimal point to be truncated.
• 1.5.A.3 Some code causes int values to be automatically cast (widened) to double values.
• 1.5.A.4 Values of type double can be rounded to the nearest integer by (int)(x + 0.5) for non-negative numbers or (int)(x - 0.5) for negative numbers.

Learning Objective 1.5.B: Describe conditions when an integer expression evaluates to a value out of range.

• 1.5.B.1 The constant Integer.MAX_VALUE holds the value of the largest possible int value. The constant Integer.MIN_VALUE holds the value of the smallest possible int value.
• 1.5.B.2 Integer values in Java are represented by values of type int, which are stored using a finite amount (4 bytes) of memory. Therefore, an int value must be in the range from Integer.MIN_VALUE to Integer.MAX_VALUE inclusive.
• 1.5.B.3 If an expression would evaluate to an int value outside of the allowed range, an integer overflow occurs. The result is an int value in the allowed range but not necessarily the value expected.

Learning Objective 1.5.C: Describe conditions that limit accuracy of expressions.

• 1.5.C.1 Computers allot a specified amount of memory to store data based on the data type. If an expression would evaluate to a double that is more precise than can be stored in the allotted amount of memory, a round-off error occurs. The result will be rounded to the representable value. To avoid rounding errors that naturally occur, use int values.
  • Exclusion statement: Other special decimal data types that can be used to avoid rounding errors are outside the scope of the AP Computer Science A course and exam.

Learning Objective 1.6.A: Develop code for assignment statements with compound assignment operators and determine the value that is stored in the variable as a result.

• 1.6.A.1 Compound assignment operators +=, -=, *=, /=, and %= can be used in place of the assignment operator in numeric expressions. A compound assignment operator performs the indicated arithmetic operation between the value on the left and the value on the right and then assigns the result to the variable on the left.
• 1.6.A.2 The post-increment operator ++ and post-decrement operator -- are used to add 1 or subtract 1 from the stored value of a numeric variable. The new value is assigned to the variable.
  • Exclusion statement: The use of increment and decrement operators in prefix form (e.g., ++x) is outside the scope of the AP Computer Science A course and exam. The use of increment and decrement operators inside other expressions (e.g., arr[x++]) is outside the scope of the AP Computer Science A course and exam.

Learning Objective 1.7.A: Identify the attributes and behaviors of a class found in the libraries contained in an API.

• 1.7.A.1 Libraries are collections of classes. An application programming interface (API) specification informs the programmer how to use those classes. Documentation found in API specifications and libraries is essential to understanding the attributes and behaviors of a class defined by the API. A class defines a specific reference type. Classes in the APIs and libraries are grouped into packages. Existing classes and class libraries can be utilized to create objects.
• 1.7.A.2 Attributes refer to the data related to the class and are stored in variables. Behaviors refer to what instances of the class can do (or what can be done with them) and are defined by methods.

Learning Objective 1.8.A: Describe the functionality and use of code through comments.

• 1.8.A.1 Comments are written for both the original programmer and other programmers to understand the code and its functionality, but are ignored by the compiler and are not executed when the program is run. Three types of comments in Java include /* */, which generates a block of comments; //, which generates a comment on one line; and /** */, which are Javadoc comments and are used to create API documentation.
• 1.8.A.2 A precondition is a condition that must be true just prior to the execution of a method in order for it to behave as expected. There is no expectation that the method will check to ensure preconditions are satisfied.
• 1.8.A.3 A postcondition is a condition that must always be true after the execution of a method. Postconditions describe the outcome of the execution in terms of what is being returned or the current value of the attributes of an object.

Learning Objective 1.9.A: Identify the correct method to call based on documentation and method signatures.

• 1.9.A.1 A method is a named block of code that only runs when it is called. A block of code is any section of code that is enclosed in braces. Procedural abstraction allows a programmer to use a method by knowing what the method does even if they do not know how the method was written.
• 1.9.A.2 A parameter is a variable declared in the header of a method or constructor and can be used inside the body of the method. This allows values or arguments to be passed and used by a method or constructor. A method signature for a method with parameters consists of the method name and the ordered list of parameter types. A method signature for a method without parameters consists of the method name and an empty parameter list.

Learning Objective 1.9.B: Describe how to call methods.

• 1.9.B.1 A void method does not have a return value and is therefore not called as part of an expression.
• 1.9.B.2 A non-void method returns a value that is the same type as the return type in the header. To use the return value when calling a non-void method, it must be stored in a variable or used as part of an expression.
• 1.9.B.3 An argument is a value that is passed into a method when the method is called. The arguments passed to a method must be compatible in number and order with the types identified in the parameter list of the method signature. When calling methods, arguments are passed using call by value. Call by value initializes the parameters with copies of the arguments.
• 1.9.B.4 Methods are said to be overloaded when there are multiple methods with the same name but different signatures.
• 1.9.B.5 A method call interrupts the sequential execution of statements, causing the program to first execute the statements in the method before continuing. Once the last statement in the method has been executed or a return statement is executed, the flow of control is returned to the point immediately following where the method was called.

Learning Objective 1.10.A: Develop code to call class methods and determine the result of those calls.

• 1.10.A.1 Class methods are associated with the class, not instances of the class. Class methods include the keyword static in the header before the method name.
• 1.10.A.2 Class methods are typically called using the class name along with the dot operator. When the method call occurs in the defining class, the use of the class name is optional in the call.

Learning Objective 1.11.A: Develop code to write expressions that incorporate calls to built-in mathematical libraries and determine the value that is produced as a result.

• 1.11.A.1 The Math class is part of the java.lang package. Classes in the java.lang package are available by default.
• 1.11.A.2 The Math class contains only class methods. The following Math class methods—including what they do and when they are used—are part of the Java Quick Reference:
  • static int abs(int x) returns the absolute value of an int value.
  • static double abs(double x) returns the absolute value of a double value.
  • static double pow(double base, double exponent) returns the value of the first parameter raised to the power of the second parameter.
  • static double sqrt(double x) returns the nonnegative square root of a double value.
  • static double random() returns a double value greater than or equal to 0.0 and less than 1.0.
• 1.11.A.3 The values returned from Math.random() can be manipulated using arithmetic and casting operators to produce a random int or double in a defined range based on specified criteria. Each endpoint of the range can be inclusive, meaning the value is included, or exclusive, meaning the value is not included.

Learning Objective 1.12.A: Explain the relationship between a class and an object.

• 1.12.A.1 An object is a specific instance of a class with defined attributes. A class is the formal implementation, or blueprint, of the attributes and behaviors of an object.
• 1.12.A.2 A class hierarchy can be developed by putting common attributes and behaviors of related classes into a single class called a superclass. Classes that extend a superclass, called subclasses, can draw upon the existing attributes and behaviors of the superclass without replacing these in the code. This creates an inheritance relationship from the subclasses to the superclass.
  • Exclusion statement: Designing and implementing inheritance relationships are outside the scope of the AP Computer Science A course and exam.
• 1.12.A.3 All classes in Java are subclasses of the Object class.

Learning Objective 1.12.B: Develop code to declare variables to store reference types.

• 1.12.B.1 A variable of a reference type holds an object reference, which can be thought of as the memory address of that object.

Learning Objective 1.13.A: Identify, using its signature, the correct constructor being called.

• 1.13.A.1 A class contains constructors that are called to create objects. They have the same name as the class.
• 1.13.A.2 A constructor signature consists of the constructor's name, which is the same as the class name, and the ordered list of parameter types. The parameter list, in the header of a constructor, lists the types of the values that are passed and their variable names.
• 1.13.A.3 Constructors are said to be overloaded when there are multiple constructors with different signatures.

Learning Objective 1.13.B: Develop code to declare variables of the correct types to hold object references.

• 1.13.B.1 A variable of a reference type holds an object reference or, if there is no object, null.

Learning Objective 1.13.C: Develop code to create an object by calling a constructor.

• 1.13.C.1 An object is typically created using the keyword new followed by a call to one of the class's constructors.
• 1.13.C.2 Parameters allow constructors to accept values to establish the initial values of the attributes of the object.
• 1.13.C.3 A constructor argument is a value that is passed into a constructor when the constructor is called. The arguments passed to a constructor must be compatible in order and number with the types identified in the parameter list in the constructor signature. When calling constructors, arguments are passed using call by value. Call by value initializes the parameters with copies of the arguments.
• 1.13.C.4 A constructor call interrupts the sequential execution of statements, causing the program to first execute the statements in the constructor before continuing. Once the last statement in the constructor has been executed, the flow of control is returned to the point immediately following where the constructor was called.

Learning Objective 1.14.A: Develop code to call instance methods and determine the result of these calls.

• 1.14.A.1 Instance methods are called on objects of the class. The dot operator is used along with the object name to call instance methods.
• 1.14.A.2 A method call on a null reference will result in a NullPointerException.

Learning Objective 1.15.A: Develop code to create string objects and determine the result of creating and combining strings.

• 1.15.A.1 A String object represents a sequence of characters and can be created by using a string literal or by calling the String class constructor.
• 1.15.A.2 The String class is part of the java.lang package. Classes in the java.lang package are available by default.
• 1.15.A.3 A String object is immutable, meaning once a String object is created, its attributes cannot be changed. Methods called on a String object do not change the content of the String object.
• 1.15.A.4 Two String objects can be concatenated together or combined using the + or += operator, resulting in a new String object. A primitive value can be concatenated with a String object. This causes the implicit conversion of the primitive value to a String object.
• 1.15.A.5 A String object can be concatenated with any object, which implicitly calls the object's toString method (a behavior that is guaranteed to exist by the inheritance relationship every class has with the Object class). An object's toString method returns a string value representing the object. Subclasses of Object often override the toString method with class-specific implementation. Method overriding occurs when a public method in a subclass has the same method signature as a public method in the superclass, but the behavior of the method is specific to the subclass.
  • Exclusion statement: Overriding the toString method of a class is outside the scope of the AP Computer Science A course and exam.

Learning Objective 1.15.B: Develop code to call methods on string objects and determine the result of calling these methods.

• 1.15.B.1 A String object has index values from 0 to one less than the length of the string. Attempting to access indices outside this range will result in a StringIndexOutOfBoundsException.
• 1.15.B.2 The following String methods—including what they do and when they are used—are part of the Java Quick Reference:
  • int length() returns the number of characters in a String object.
  • String substring(int from, int to) returns the substring beginning at index from and ending at index to - 1.
  • String substring(int from) returns substring(from, length()).
  • int indexOf(String str) returns the index of the first occurrence of str; returns -1 if not found.
  • boolean equals(Object other) returns true if this corresponds to the same sequence of characters as other; returns false otherwise.
  • int compareTo(String other) returns a value < 0 if this is less than other; returns zero if this is equal to other; returns a value > 0 if this is greater than other. Strings are ordered based upon the alphabet.
  • Exclusion statement: Using the equals method to compare one String object with an object of a type other than String is outside the scope of the AP Computer Science A course and exam.
• 1.15.B.3 A string identical to the single element substring at position index can be created by calling substring(index, index + 1).