Java Identifiers and Variables Quiz

Identifiers in Java

• A Java identifier is the name of a variable or other item defined in a program.
• An identifier must not start with a digit and can only contain letters, digits, or the underscore (_) symbol.
• The symbol $ is also allowed, but it's reserved for special purposes only.

Keywords in Java

• Keywords are a special class of identifiers with a predefined meaning in Java.
• Keywords cannot be used as names for variables or anything else.

Variables and Declaration

• Every variable in a Java program must be declared before it is used.
• When declaring a variable, you specify the type of data it will store.
• Syntax: Type Variable_1, Variable_2,...;
• Examples: int count, number;, char answer;, double speed, distance;

Primitive Datatypes

• No specific details mentioned in the text.

Assignment Statements

• The equal sign (=) is used as the assignment operator.
• An assignment statement always consists of a variable on the left-hand side and an expression on the right-hand side.
• An assignment statement ends with a semicolon.
• The expression on the right-hand side can be a variable, a number, or a complicated expression.
• Examples: distance = rate * time;, count = count + 2;

Assignment Statements with Primitive Types

• When a variable of a primitive type is on the left-hand side of an assignment, the expression on the right-hand side is evaluated first.
• Then, the variable is set equal to the evaluated value.

Initializing Variables

• Assigning a value to a variable is known as initialization.
• Combine the declaration and an assignment statement, e.g., int count = 0;, double speed = 65.5;, char grade = 'A';

Short Hand Assignments operators

• No specific details mentioned in the text.

Assignment Compatibility

• In general, a value of one type cannot be stored in a variable of another type.
• Exceptions: an int value can be stored in a double type.
• A value of any type can be assigned to a variable of any type that appears to the right of it in the list: byte, short, int, long, float, double, char.
• An explicit type cast is required to assign a value of one type to a variable whose type appears to the left of it on the list (e.g., double to int).

Constants

• A constant (or literal) is an item in Java with a specific value that cannot change.
• Constants of an integer type cannot be written with a decimal point.
• Constants of a floating-point type can be written in ordinary decimal fraction form or in scientific notation.
• Constants of type char are expressed by placing a single character in single quotes.