APCSA 1.3 — Expressions and Output (Java)

Overview

An expression combines values, variables, operators, and method calls to produce a single value. Output displays information to the user, typically with System.out.print() or System.out.println().

1) Expressions

Expressions range from a literal like 10 to complex formulas like (a + b) * c / 2. Java follows operator precedence and type conversion rules.

int sum = 5 + 3 * 2;   // 11
int remainder = 10 % 3; // 1

String name = "Mr. " + "Cusack"; // "Mr. Cusack"

boolean result = (5 > 3) && (2 < 4); // true
// Relational: > < >= <= == !=
// Logical:    &&, ||, !

2) Operator Precedence

Determines evaluation order. Use parentheses for clarity.

int a = 5 + 3 * 2;     // 11
int b = (5 + 3) * 2;   // 16

3) Type Conversion (Casting)

Java promotes types automatically when mixing int and double. Use casting to control results.

double avg1 = (3 + 4 + 5) / 3;    // 12 / 3 = 4  (integer division → 4.0)
double avg2 = (3 + 4 + 5) / 3.0; // 12 / 3.0 = 4.0 (double)
double avg3 = (double)(3 + 4 + 5) / 3; // 12.0 / 3 = 4.0

Note: If all operands of / are int, Java performs integer division and truncates decimals.

4) Output Statements

Use System.out.print() (no newline) and System.out.println() (adds newline).

System.out.print("Hello");
System.out.println(" World!");
// Output: Hello World!

5) Escape Sequences

System.out.println("Hello\nWorld!");
/* Output:
Hello
World!
*/

6) Combining Expressions and Output

int age = 17;
System.out.println("You are " + age + " years old.");
// You are 17 years old.

7) Common Pitfalls

• Integer division truncates: 5 / 2 is 2, not 2.5.
• Concatenation order matters:

  System.out.println("Sum: " + 2 + 3);   // Sum: 23
  System.out.println("Sum: " + (2 + 3)); // Sum: 5

• Use parentheses to control evaluation order and readability.

✅ Summary

Tip: Add small, runnable snippets in your IDE so students can see actual outputs.