University of Washington, AP/CS A

Lab 2: Expressions

lab document created by Marty Stepp, Stuart Reges and Whitaker Brand

Today's lab

Goals for this lab:

write and evaluate expressions to compute numeric values
write and evaluate expressions that involve string concatenation with numeric values
write and evaluate boolean expressions
note that a yellow response indicates that you have the correct response but not in the correct format (e.g., entering 17 for a double value instead of 17.0 or not including quotation marks around a string)
Where you see this icon, you can click it to check the problem in Practice-It!

Expressions

Recall that Java has expressions to represent math and other computations. Expressions may use operators, which are evaluated according to rules of precedence. Every expression produces a value of a given type.

Type	Description	Expression Example	Result
`int`	integers (up to 2³¹ - 1)	`3 + 4 * 5`	`23`
`double`	real numbers (up to 10³⁰⁸)	`3.0 / 2.0 + 4.1`	`5.6`
`String`	text characters	`"hi" + (1 + 1) + "u"`	`"hi2u"`

Exercise : Expressions (2.1)

Write the results of each of the following expressions. If you're stuck, ask a TA or neighbor.

`12 / 5`		2
`12.0 / 5`		2.4
`12 / 5 + 8 / 4`		4
`3 * 4 + 15 / 2`		19
`42 % 5 + 3 % 16***`		5

***Hint: Suppose you have 3 apples, and you distribute them among 16 people so that everyone gets the same number of (whole) apples. How many (whole) apples does each person get? How many apples do you have left over?

Exercise : More expressions (2.1)

Write the results of each of the following expressions.

Some of these expressions include String concatenation. When the result of the expression evaluates to a String, put "quotation marks" around the result:

`"x" + 2`	"x2"	`// Add the other quote to get the correct answer`
`2 + 6 + "cse 142"`	"8cse 142"
`"cse 142" + 2 + 6`	"cse 14226"
`1 + 9 / 2 * 2.0`	9.0
`46 / 3 / 2.0 / 3 * 4/5`	2.0

Exercise : Expressions

For each expression in the left-hand column, indicate its value in the right-hand column. Be sure to list a constant of appropriate type (e.g., 7.0 rather than 7 for a double, Strings in quotes).

`4 * (2 + 4) - 3 * 5`		9
`54 % 10 + 8 * 3 % 9`		10
`3 * 2 + 4 + "+" + 2 + 3 * 4`		"10+212"
`2.3 * 3 + 19 / 5 / 2 + 6.0 / 5`		9.1
`108 / 20 * 3 / 4 / 2.0 + 1.0 / 2`		2.0

Exercise : Expressions

For each expression in the left-hand column, indicate its value in the right-hand column. Be sure to list a constant of appropriate type (e.g., 7.0 rather than 7 for a double, Strings in quotes).

If you've forgotten how to tackle expressions problems, check out lab 2 for a recap!

`12/5 + 8/4`		4
`2.5 * 2 + 17/4`		9.0
`41 % 15 % 7 + 17 % 3`		6
`21/2 + "7 % 3" + 17 % 4`		"107 % 31"
`46/3/2.0/3 * 4/5`		2.0

Exercise : Expressions

For each expression in the left-hand column, indicate its value in the right-hand column. Be sure to list a constant of appropriate type (e.g., 7.0 rather than 7 for a double, Strings in quotes).

`1 + 9 / 2 * 2.0`		9.0
`5.0 / (3125 % 2) + 2 * (5 / 3)`		7.0
`6 % 17 + 9 % 3 + 22 / 4 / 2.0`		8.5
`"[" + 2 + 4 * 2.0 + "]" + 3`		"[28.0]3"
`!(3 < 2) && (4.3 > 3 \|\| 3 < 2)`		true

Exercise : Expressions

For each expression in the left-hand column, indicate its value in the right-hand column. Be sure to list a constant of appropriate type (e.g., 7.0 rather than 7 for a double, Strings in quotes).

`3 + 3 * 8 - 2`		25
`109 % 100 / 2 + 3 * 3 / 2.0`		8.5
`1 - 3 / 6 * 2.0 + 14 / 5`		3.0
`1 + "x" + 11 / 10 + " is" + 10 / 2`		"1x1 is5"
`10 % 8 * 10 % 8 * 10 % 8`		0

Exercise : Boolean Expressions

Write the result of each expression as either true or false, given the following variables.

int x = 12;
int y = 7;
int z = 28;
String s = "mid term";

`x < 14`		true
`!(x % 2 < 1)`		false
`x < y \|\| x < z`		true
`z / x < x / y * x`		true
`s.length() == y`		false
`s.toUpperCase().equals("MID TERM")`		true
`!s.equals("mid term") \|\| x * y != z`		true
`s.substring(z / x).length() > y`		false