ACSA Exam Prep
Unit 1 · Using Objects and Methods · Topic 1.3

Expressions and Output

Skill 2.ASkill 3.ASkill 3.D

Big idea: Arithmetic in Java mostly works like math class, with two big surprises: dividing two ints throws away the remainder, and + switches to joining text as soon as a String is involved.

Learning objectives
  • Develop code to generate output and determine the result that would be displayed.
  • Develop code to utilize string literals and determine the result of using string literals.
  • Develop code for arithmetic expressions and determine the result of these expressions.

print vs. println

System.out.print displays its value and keeps the cursor on the same line. System.out.println displays its value and then moves to a new line.

Code
System.out.print("A");
System.out.print("B");
System.out.println("C");
System.out.println("D");
Output
ABC
D

String literals and escape sequences

A string literal is text in double quotes. To put a special character inside, use an escape sequence: \" for a double quote, \\ for a backslash, and \n for a new line.

Code
System.out.println("She said \"hi\"");
System.out.println("C:\\temp");
System.out.println("line 1\nline 2");
Output
She said "hi"
C:\temp
line 1
line 2

Integer division and remainder

When both operands are int, the result is an int: / keeps only the whole-number part (it truncates). If at least one operand is a double, the result is a double.

% (mod) gives the remainder. It is handy for even/odd tests (n % 2 == 0), for "every kth" patterns, and for pulling digits off a number (n % 10 is the last digit, n / 10 drops it).

Code
System.out.println(17 / 5);
System.out.println(17 % 5);
System.out.println(17 / 5.0);
System.out.println(4 % 7);
System.out.println(1234 % 10 + " " + 1234 / 10);
Output
3
2
3.4
4
4 123

Precedence and left-to-right +

*, /, and % happen before + and -. Operators with the same precedence go left to right, and parentheses override everything.

+ adds numbers, but once the left side is a String, it concatenates. Work left to right one operator at a time.

Code
System.out.println(2 + 3 * 4);
System.out.println(10 - 4 - 3);
System.out.println(20 / 4 * 2);
System.out.println(1 + 2 + "3" + 4 + 5);
System.out.println("Sum: " + (4 + 5));
Output
14
3
10
3345
Sum: 9
Key points
  • println ends the line; print doesn't.
  • Escape sequences: \", \\, \n.
  • int / int truncates: 7 / 2 is 3. Any double operand gives a double: 7 / 2.0 is 3.5.
  • % gives the remainder: 17 % 5 is 2, and 4 % 7 is 4.
  • * / % before + -; ties go left to right.
  • Dividing an int by integer zero throws an ArithmeticException.
Watch out
  • String concatenation is left to right: 1 + 2 + "3" is "33", but "3" + 1 + 2 is "312".
  • % has the same precedence as * and /, not lower.
  • When the left number is smaller, a % b is just a: 3 % 8 is 3.
Exam tip
  • Trace mixed expressions one operator at a time and write the type of each intermediate result (int, double, or String).
Quick check
What is printed?
System.out.println(7 / 2 * 2.0);
Show answer
6.0. First 7 / 2 is 3 (int division), then 3 * 2.0 is 6.0.
What is printed?
System.out.println("" + 4 + 4 + (4 + 4));
Show answer
448. The empty string makes the first + concatenate; the parentheses add first.
Not on the exam
  • Expressions that produce Infinity or NaN.
  • Using % with a negative left operand or a right operand ≤ 0.
  • Dividing by zero when one value is a double.
Practice 1.3 (15 questions)