(4) A popular way of formatting output in Java is the print format
function, originated from the C and C++ languages, that takes the
following form:
• The first parameter is a format string that specifies the format of the
output. Each format specifier starts with a percent sign (%) and
finishes with a letter that determines the type of output.
• The remaining parameters, i.e., the arguments, are the values to be
printed out.
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System.out.printf(“String”, [arguments]);
• For example, when the following statement is executed
it produces the output:
• The meanings of format specifier:
• “10” – the minimum number of characters in the output
• “2” – the number of digits after the decimal point
• “f” – the output is in floating-point form
• “6.02235” – the number to be printed
• Unless specified otherwise, the number is right justified
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System.out.printf(“%10.2f”, 6.02235);
_ _ _ _ _ _ 6.02
• Besides the floating point format, there are some common format
specifiers that are useful in Java programming
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• Format specifiers can be combined with other characters in the
format string, making it quite handy to insert values into an output
string.
• For example: The following snippet
yields the output:
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int x = 17, y = 42;
System.out.printf(“The product of %d and %d is %d”, x, y, x*y);
The product of 17 and 42 is 714
• Example: Execute the following code
• The output:
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double price = 19.5;
int quantity = 2;
String item = “Widgets”;
System.out.printf(“%10s sold:%4d at $%5.2f. Total = $%1.2f”,
item, quantity, price, quantity*price);
_ _ _ Widgets sold:_ _ _ 2 at $19.50. Total = $39.00
%10s %4d %5.2f
%1.2f
• In addition, flags can be added to further control the appearance of
the formatted output.
• Some common flags are tabulated below:
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• For example, the following statements
yield the outputs
• Yet
give
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System.out.printf(“%,1.2f”, 10000.0 / 3.0);
3,333.33
System.out.printf(“%, 1.2f”, 10000.0 / 3.0);
System.out.printf(“%,+1.2f”, 10000.0 / 3.0);
System.out.printf(“%,+1.2f”, -10000.0 / 3.0);
System.out.printf(“%,(1.2f”, -10000.0 / 3.0);
_ 3,333.33 +3,333.33
-3,333.33
(3,333.33)
(5) (Optional) Formatting output can be achieved using field widths.
There are three types of variables whose field widths can be adjusted.
• (i) Formatting strings: A number after the string will create a left
justified partition.
• For example, the line
gives the output below:
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print(“Strings”, integer);
System.out.print(“Bob A”, 7);
Bob _ A _ _
Altogether seven spaces from the left
• (ii) Formatting integers: a number after the integer will create a right
justified partition.
• For example, the code below
generates the output
• Think: What will be the output when the following line is run?
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System.out.print(123, 8);
_ _ _ _ _ 123
Altogether 8 spaces from the right
System.out.print(215, 6); System.out.print(56, 4);
• (iii) Formatting decimals: the first number after the value will create a
right justified partition, and the second number is how many spaces
after the decimal to round to.
• For example, the statement
prints out
• The statement
on the other hand yields
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System.out.print(123.56, 8, 1);
_ _ _ 123.6
Altogether 8 partitions
1 decimal place
System.out.print(123.56, 9, 4);
_ 123.5600
• Example: What will be the output when the following program is run?
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System.out.println(“12345678901234567890”);
System.out.print(“Hey”, 5);
System.out.print(“Whats Up”, 12);
System.out.println(“Doc”);
System.out.println(512, 5);
System.out.print(67.8, 6, 1);
System.out.println(765.987, 7, 2);
System.out.println(765.987, 8, 1);
System.out.println(765.987, 1, 3);
System.out.println(765.987, 10, 5);
• Some reminders:
1. In formatting strings, integers or decimals, if the field width is too
small to fit in the assigned value, it will be ignored.
2. A string and a number cannot be formatted in the same print() or
println() statement.
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System.out.print(“Nice Day!”, 12);
System.out.print(“Nice Day!”, 5);
Nice _ Day! _ _ _
Nice _ Day!
System.out.println(“Hi there” + 67.89, 5, 1);
System.out.print(“Hi there”);
System.out.println(67.89, 5, 1);
Error!
Hi there 67.9
• Note: The direct manipulation of field width requires a specific class
that is not included in the Java package, and is therefore not
applicable in our class.
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(h) Input
• Unlike output which can be formatted rather straightforwardly,
reading input is quite tricky in Java.
• In order to read console input, we need to construct a Scanner that is
attached to System.in:
• Here in is the object that allows for console input. This object can
then be used in conjunction with various methods in Scanner class to
read input.
• For example:
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Scanner in = new Scanner(System.in);
String name = in.nextLine();
• The Scanner class is defined within the java.util package. Therefore, it
has to be imported at the beginning:
• There are several common methods in Scanner class:
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import java.util.Scanner;
Method Function
nextLine() Read in the next line of input
next() Read in the next word of input
nextInt() Read in an integer
nextDouble() Read in a floating point value
