Question

State whether each of the following is true or false. If false, explain why. a) Java operators are evaluated from left to right. b) The following are all valid variable names: _under_bar_s \(m 928134,\) t5, j7, her_saless, his_saccount_total, a, bs, c, zand z2. c) A valid Java arithmetic expression with no parentheses is cvaluated from left to right. d) The following are all invalid variable names: \(3 g, 87,67 h 2,\) h22 and \(2 \mathrm{h}\).

Short answer

a) False; b) False; c) True; d) False.

Step-by-step solution

Analyze Statement (a)

Statement (a) says "Java operators are evaluated from left to right." While Java operators like addition (+) and subtraction (-) follow a left-to-right associativity, operators like assignment (=) are evaluated right-to-left. Therefore, this statement is false because it oversimplifies how operators are evaluated in Java.

Analyze Statement (b)

In statement (b), the variable names are _under_bar_s, m 928134, t5, j7, her_saless, his_saccount_total, a, bs, c, zand z2. All of these names are valid except "m 928134" because it contains a space, which is not allowed in Java variable names. Therefore, this statement is false.

Analyze Statement (c)

Statement (c) claims "A valid Java arithmetic expression with no parentheses is evaluated from left to right." This is true. Operators in Java are evaluated based on precedence rules, but within the same precedence, they do follow left-to-right associativity (except for operators such as assignment). So, this statement is true but need to be careful about operator precedence.

Analyze Statement (d)

Statement (d) claims that "The following are all invalid variable names: 3g, 87,67 h 2, h22 and 2h." The names "3g" and "2h" are invalid because variable names cannot start with a number. "87,67 h 2" is also invalid because it contains spaces and a comma. However, "h22" is a valid variable name because it starts with a letter and contains alphanumeric characters with no spaces or special symbols. Therefore, this statement is false.

Key concepts

Variable Naming Conventions

Variable naming conventions in Java play a crucial role in writing readable and maintainable code. A variable name must start with a letter, a dollar sign ($), or an underscore (_), but it cannot start with a number. For instance, "3g" and "2h" are invalid because they begin with a digit.

• Variable names should not contain spaces. "m 928134" is invalid due to the space.
• The name can only include alphanumeric characters and underscores. Special characters like a comma are not allowed.
• Java is case-sensitive, so "Variable", "variable", and "VARIABLE" would be considered distinct names.

Following these rules ensures that programmers avoid syntax errors and write intuitive code. Choosing descriptive names also helps with readability, making your code easier for others (and yourself) to understand.

Operator Precedence

Understanding operator precedence is essential when evaluating expressions in Java. Operators have priority levels, determining the order in which they're applied. For instance, multiplication and division operators have higher precedence than addition and subtraction. This means in an expression like "3 + 4 * 2", the multiplication happens first, resulting in "3 + 8" rather than "7 * 2".

Within the same precedence level, associativity rules determine the order of evaluation. The general rule is:

• Left-to-right associativity for most operators, like addition, subtraction, multiplication, and division.
• Right-to-left associativity for the assignment operators.

Keep precedence in mind to avoid unexpected results, and use parentheses "()" to explicitly define the desired order of evaluation.

Associativity of Operators

Associativity refers to the direction in which operators of the same precedence are evaluated. In Java, most arithmetic operators are evaluated left-to-right, known as left-to-right associativity. This means within an expression without parentheses, operators would be evaluated starting from the leftmost side moving to the right.

Contrarily, some operators like assignment '=' and unary operators such as increment '++' and decrement '--' have right-to-left associativity. This property allows operations to be applied starting from the rightmost side. Understanding associativity helps avoid logical errors in complex expressions.

• Left-to-right associativity: Addition (+), subtraction (-), multiplication (*).
• Right-to-left associativity: Assignment (=), ternary (?:).

Recognizing the associativity of operators ensures you write correct and predictable Java expressions.

Arithmetic Expressions in Java

Arithmetic expressions in Java consist of operands (values) and operators (symbols that perform operations). Java uses standard arithmetic operators like addition (+), subtraction (-), multiplication (*), and division (/). Understanding how these operators work is fundamental to mathematical calculations in any Java program.

Parentheses can be used to change the default precedence of operations; they have the highest precedence in expressions. If an expression includes operators with the same precedence, associativity rules, usually left-to-right, decide the order.

• "3 + 5 * 2" evaluates as "3 + (5 * 2)" because multiplication has higher precedence than addition.
• "(3 + 5) * 2" ensures addition occurs before multiplication and evaluates to 16.

Understand these concepts to perform accurate computations and write efficient Java programs.