1.3 Expressions and Output

1. Output: print and println

System.out.print and System.out.println display information on the computer display. System.out.println moves the cursor to a new line after the information has been displayed; System.out.print does not 1.3.A.1. System.out.println(); with nothing inside just ends the line.

System.out.print("Total: ");
System.out.println(7 + 3);    // 10, after "Total: "
System.out.println("7" + 3);  // 73 (text joined, not added)
System.out.print("A");
System.out.print("B");
System.out.println();         // just ends the line
System.out.println("C");

Output:

Total: 10
73
AB
C

Watch out: print does not add a space. If you want one, put it inside the quotes, as in "Total: ".

2. Literals and string literals

A literal is the code representation of a fixed value, such as 42, 3.5 or true 1.3.B.1. A string literal is a sequence of characters enclosed in double quotes, such as "Game over" 1.3.B.2.

A literal’s form sets its type: 7 is an int, 7.0 is a double, "7" is a String and true is a boolean. So 7 / 2 uses int division but 7.0 / 2 does not 1.3.B, 1.3.C.

System.out.println(7 / 2);
System.out.println(7.0 / 2);
System.out.println("7 / 2");

Output:

3
3.5
7 / 2

The last line prints the characters exactly as written, because they are inside a string literal. Java does not calculate anything inside quotes.

3. Escape sequences

Escape sequences are special sequences of characters inside a string. They start with a backslash \ and have a special meaning in Java. The 3 escape sequences in this course are \" (double quote), \\ (backslash) and \n (newline) 1.3.B.3.

Each escape sequence stands for one character in the String, so "a\nb".length() is 3 (length() is in topic 1.15).

System.out.println("She said \"go\"\nC:\\temp");
System.out.println("a\nb".length());

Output:

She said "go"
C:\temp
3

Watch out: a single \ inside a string always starts an escape sequence. In "C:\temp", Java reads \t as a tab (outside the course), so the backslash is never printed; with most other letters, such as "C:\data", the code does not compile. To print one backslash, write two: \\.

4. Arithmetic expressions

An arithmetic expression is made of numeric values, variables and operators, and it can have type int or double 1.3.C.1. The 5 arithmetic operators are +, -, *, / and % (remainder) 1.3.C.2.

• An operation with two int values evaluates to an int. An operation with at least one double value evaluates to a double 1.3.C.2.
• Dividing two int values gives only the integer portion of the quotient. Dividing when at least one value is a double gives the full quotient 1.3.C.3.
• The remainder operator % computes the remainder when one number a is divided by another number b 1.3.C.4.
• int division drops the decimal part, so the result moves toward zero: -7 / 2 is -3, not -4.

Expression	Value	Why
17 / 5	3	int / int keeps only the integer part
17 % 5	2	remainder of 17 divided by 5
17 / 5.0 and 17.0 / 5	3.4	at least one double, so the result is a double
2 + 3 * 4	14	*, /, % before +, -
(2 + 3) * 4	20	parentheses change the grouping
10 - 4 - 3	3	same precedence: left to right
8 % 3 * 2	4	same precedence: 8 % 3 is 2, then * 2

System.out.println(17 / 5);
System.out.println(17 % 5);
System.out.println(17 / 5.0);
System.out.println(17.0 / 5);
System.out.println(-7 / 2);
System.out.println(2 + 3 * 4);
System.out.println((2 + 3) * 4);
System.out.println(10 - 4 - 3);
System.out.println(8 % 3 * 2);

Output:

3
2
3.4
3.4
-3
14
20
3
4

Outside the course: % with a negative first value or with a divisor of 0 or less, double division by zero, and results such as infinity or NaN (not a number).

5. Operator precedence

Operator precedence is the order in which Java groups operators. At compile time, values are associated with operators by precedence. Parentheses change the grouping. Multiplication, division and remainder have precedence over addition and subtraction, and operators with the same precedence are evaluated from left to right 1.3.C.5.

Higher rows group first (they hold their operands more tightly). Within rows 3 and 4, Java works left to right. The course framework states rows 1, 3 and 4; rows 2 and 5 are how Java works, and they explain the casting and assignment rules in topics 1.4 to 1.6.

Order	Operators	Example	Value
1	( ) parentheses	(2 + 3) * 4	20
2	one-operand operators: -x (negation), casts (int) and (double)	(int) 3.9 * 2	6 (the cast applies to 3.9 only)
3	* / %	10 - 4 * 2	2
4	+ - (two operands)	10 - -3	13 (subtract negative 3)
5	= += -= *= /= %=	x *= 2 + 3	the whole right side first (topic 1.6)

System.out.println((int) 3.9 * 2);
System.out.println((int) (3.9 * 2));
System.out.println(10 - -3);
System.out.println(7 + 9 / 4 * 2);

Output:

6
7
13
11

In the last line, 9 / 4 is 2 (int division), 2 * 2 is 4, and 7 + 4 is 11.

Background (not tested): unary and binary operators. The values an operator works on are its operands. A unary operator has one operand: -x, (int) x, x++ (see topic 1.6). A binary operator has two: a - b, a * b. The same symbol can do different jobs. - is negation in -x but subtraction in a - b. + adds when both operands are numbers but joins text when either operand is a String (concatenation, see topic 1.15), and because Java works left to right, 1 + 2 + "!" is "3!" while "!" + 1 + 2 is "!12". The words unary, binary and operand are not official course wording, but they help you read any expression.

System.out.println(1 + 2 + "!");
System.out.println("!" + 1 + 2);

Output:

3!
!12

6. Dividing by zero

An attempt to divide an integer by the integer zero results in an ArithmeticException 1.3.C.6. The code compiles, but the program stops when the division runs.

int players = 0;
System.out.println("Splitting 20 points");
System.out.println(20 / players);

Output:

Splitting 20 points
Exception in thread "main" java.lang.ArithmeticException: / by zero

Outside the course: dividing by zero when one of the values is a double.

7. Using / and % together

/ and % together split a number into parts 1.3.C:

• n % 2 is 0 for even numbers and 1 for odd ones (for n of 0 or more).
• n % 10 gives the last digit and n / 10 removes it, so 347 % 10 is 7 and 347 / 10 is 34.
• minutes / 60 and minutes % 60 split 135 minutes into 2 hours and 15 minutes.

int minutes = 135;
System.out.println(minutes / 60 + " h " + minutes % 60 + " min");
int code = 347;
System.out.println(code % 10);
System.out.println(code / 10);
System.out.println(code % 2);

Output:

2 h 15 min
7
34
1

These moves return in Unit 2 and in free-response questions.