Expression Statements

Expressions

An expression is a combination of variables, literals, operators, and method calls that evaluates to a single value. It represents a computation and always produces a result of a specific data type (e.g., int, boolean, String).

Key Characteristics:

• Must evaluate to a value.
• Can be part of a larger expression or statement.
• Can include operators (e.g., +, -, ==) and operands (e.g., variables, constants).
• Example: 5 + 3 evaluates to 8.

public class Main {
    public static void main(String[] args) {
        int a = 10, b = 5;
        System.out.println(a + b);          // 15 (arithmetic)
        System.out.println(a > b);          // true (relational)
        System.out.println(a > 0 && b < 10); // true (logical)
        System.out.println(Math.max(a, b)); // 10 (method call)
        int c = a + b;                      // c = 15 (assignment expression)
    }
}

• Note: Parentheses () can be used to control the order of evaluation in complex expressions.

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Statements

A statement is a complete unit of execution in Java that performs an action. Unlike expressions, statements don’t necessarily produce a value—they instruct the program to do something (e.g., assign a value, control flow, or call a method).

Key Characteristics:

• Ends with a semicolon (;) in most cases (except block statements).
• Can contain expressions.
• Represents an actionable command.

Types of Statements:

1. Expression Statements:
   • An expression followed by a semicolon becomes a statement.
   • Example: x = 5; (assigns 5 to x).
   • Example: System.out.println("Hello"); (calls a method).
2. Declaration Statements:
   • Declare variables and optionally initialize them.
   • Example: int x; or int x = 10;.
3. Control Flow Statements:
   • Alter the execution path of a program.
   • Types:
     • Conditional: if, if-else, switch.
     • Looping: for, while, do-while.
     • Branching: break, continue, return.
   • Example: if (x > 0) System.out.println("Positive");.
4. Block Statements:
   • Group multiple statements within curly braces {}.
   • Example:

{
    int x = 5;
    System.out.println(x);
}

5. Empty Statement:
   • A standalone semicolon (;) that does nothing.
   • Example: for (int i = 0; i < 5; i++); (loop does nothing).

Examples:

public class Main {
    public static void main(String[] args) {
        // Expression Statement
        int x = 10;                     // Assignment
        System.out.println(x);          // Method call
 
        // Declaration Statement
        double y = 5.5;
 
        // Control Flow Statement
        if (x > 0) {
            System.out.println("x is positive"); // Block statement
        }
 
        // Loop Statement
        for (int i = 0; i < 3; i++) {
            System.out.println(i);
        }
    }
}

• Output:

10
x is positive
0
1
2

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Key Differences Between Expressions and Statements

Aspect	Expression	Statement
Purpose	Evaluates to a value	Performs an action
Result	Always produces a value	May or may not produce a value
Examples	5 + 3, x > y, Math.sqrt(4)	x = 5;, if (x > 0) { ... }
Semicolon	Not required unless part of a statement	Usually ends with ; (except blocks)
Composition	Can be part of a statement	Can contain expressions

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