This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Slide 1
CS0007: Introduction to Computer Programming The switch
Statement, DecimalFormat, and Introduction to Looping
Slide 2
Review You can test a series of condition with the if-else if
statement Nesting is enclosing one structure inside of another.
Binary logical operators combine two boolean expressions into one.
Binary logical operators: && || Unary logical operator:
!
Slide 3
Review What does the == operator compare when the operands are
strings? Their references What should you use instead of logical
operators when comparing strings? equals compareTo A variable has
block-level scope if It is declared inside of a block A variable
that is declared inside of a block has scope beginning at Its
declaration A variable that is declared inside of a block has scope
ending at The end of the block in which it was declared
Slide 4
The switch Statement It is often the case that you want the
value of a single variable decide which branch a program should
take: if (x == 1) statement or block 1 if else (x == 2) statement
or block 2 if else (x == 3) statement or block 3 else statement or
block 4 This is tedious and not very aesthetically pleasing. Java
provides a structure that lets the value of a variable or
expression decide which branch to take This structure is called a
switch statement.
Slide 5
The switch Statement General form of a switch statement: switch
(SwitchExpression) { case CaseExpression1: //One or more statements
break; case CaseExpression2: //One or more statements break;
default: //One or more statements } switch keyword that begins a
switch statement SwitchExpression a variable or expression that has
to be either char, byte, short, or int. case keyword that begins a
case statement (there can be any number of case statements)
CaseExpression1 a literal or final variable that is of the same
type as SwitchExpression.
Slide 6
The switch Statement General form of a switch statement: switch
(SwitchExpression) { case CaseExpression1: //One or more statements
break; case CaseExpression2: //One or more statements break;
default: //One or more statements } Inside a case statement, one or
more valid programming statements may appear. After the
statement(s) inside of a case statements block, often the keyword
break appears. After all of the case statements, there is the
default case, which begins with the keyword default.
Slide 7
The switch Statement General form of a switch statement: switch
(SwitchExpression) { case CaseExpression1: //One or more statements
break; case CaseExpression2: //One or more statements break;
default: //One or more statements } What this does is compare the
value of SwitchExpression to each CaseExpression s. If they are
equal, the statements after the matching case statement are
executed. Once the break keyword is reached, the statements after
the switch statements block are executed. break is a keyword that
breaks the control of the program out of the current block. If none
of the CaseExpression s are equal to SwitchExpression, then the
statements below the default case are executed.
Slide 8
The switch Statement if (x == 1) y = 4; if else (x == 2) y = 9;
else y = 22; Is the same as switch (x) { case 1: y = 4; break; case
2: y = 9; break; default: y = 22; }
Slide 9
switch Statement Example New Topics: The switch Statement
Slide 10
The switch Statement Notes The CaseExpression of each case
statement must be unique. The default section is optional. Again,
the SwitchExpression and all of the CaseExpression s must be either
char, byte, short, or int. Without the break; at the end of the
statements associated with a case statement, the program falls
through to the next case statements statements, and executes them.
If this is what you actually want, then leave out the break;, but
often it isnt. Why doesnt default statement have a break; at the
end?
Slide 11
The DecimalFormat Class Java has a default way of displaying
floating-point numbers, but it is often the case you want to
display them in a particular format The Java API provides a class
to do this called DecimalFormat. You create a DecimalFormat object
much like how you created a Scanner object. DecimalFormat
identifier = new DecimalFormat(formattingPattern); Also like when
you create Scanner object, you must include an import statement
before the class header: import java.text.DecimalFormat;
Slide 12
The DecimalFormat Class formattingPattern is an argument passed
to the DecimalFormat constructor that tells it what format to
display the floating-point numbers. Each character in the
corresponds with a position in the number # - specifies that a
digit should be displayed if present 0 - specifies that a digit
should be displayed if present, but if not 0 should be displayed %
- placed at the end to multiply the number by 100 and place the %
character at the end. To apply the format to a number, you must use
the format method of the DecimalFormat object.
decimalformatIdentifier.format(floatingPointNumber)
Slide 13
DecimalFormat Example New Topics: DecimalFormat class
Slide 14
The printf method Another way to format output is with the
printf method from the out object in the System class.
System.out.printf(FormatString, ArgumentList); This is a formatting
method taken from old C formatting It is very powerful, and
somewhat easy to use. The book goes over some examples of how it
can be used. Also there are many, many examples of how to use this
online.
Slide 15
Loops So far we have used decision structures to determine
which statements are executed and which are not depending on a
condition. We used this for: Validation General control flow More
specifically, weve used decision structures to execute statements
that follow the condition one or zero times. What if we want the
user to keep trying to put in valid input until she succeeds? How
would we do this with decision structures? Can we? Answer: No
Solution: Loops A loop is a control structure that causes a
statement or group of statements to repeat. We will discuss three
(possibly four) looping control structures. They differ in how they
control the repitition.
Slide 16
The while Loop The first looping control structure we will
discuss is the while loop. General Form: while (BooleanExpression)
Statement or Block First, the BooleanExpression is tested If it is
true, the Statement or Block is executed After the Statement or
Block is done executing, the BooleanExpression is tested again If
it is still true, the Statement or Block is executed again oThis
continues until the test of the BooleanExpression results in false.
Note: the programming style rules that apply to decision statements
also apply.
Slide 17
The while Loop Flowchart Boolean Expression Statement or Block
True False
Slide 18
while Loop Example New Topics: while Loop Here, number is
called a loop control variable. A loop control variable determines
how many times a loop repeats. Each repetition of a loop is called
an iteration. The a while loop is known as a pretest loop, because
it tests the boolean expression before it executes the statements
in its body. Note: This implies that if the boolean expression is
not initially true, the body is never executed. number