Chapter 2 topics
Concept
# on Java Subset Required for AP Exam
print and println
10. Testing of output is restricted to
System.out.print and System.out.println
String literals & Concatenation
8. String concatenation + is part of the AP
Java subset
Escape sequences: produce backslash,
double quotes, new line
9. The escape sequences inside strings
\\, \", \n are part of the AP Java subset.
Data types
1, 7. primitive types int, double, and
boolean
Variables and assignment
4
Arithmetic Expressions
2, 3, 4, 5, 6
Order of precedence
2.
Objects & Classes
println & print
System.out.println(“ Will print this statement
and then return to a new line”);
System.out.print( “Will print this statement and
stay on the same line” );
System.out.println(“ I’m on the line with the
statement above.”);
// ************************************************************************
// PrintPrintln.java
Author: Gail Chapman
// This program demonstrates Println and Print
// ***********************************************************************
public class PrintPrintln
{
public static void main(String[]args)
{
System.out.println("Will print this statement and then return to a new line");
System.out.print( "Will print this statement and stay on the same line" );
System.out.println(" I’m on the line with the statement above.");
}
}
Output:
Will print this statement and then return to a new line
Will print this statement and stay on the same line I’m on the line with the statement above.
String literals & Concatenation
String refers to a string of characters that make up
words.
String is a class. It is not a primitive data type.
Every String literal is an object.
String literals are words in quotation marks.
“This is a String literal”;
Concatenation
The concatenation operator used with Strings is
the plus sign +
The + sign is also used for arithmetic operations.
The + sign joins:
Strings and other Strings
(“This is a String ” + “ and another String”);
Strings & Numbers
Need to be careful to get correct output from numbers.
System.out.println(“We want to add “ + 10 + 15);
What is the output:
The compiler starts at the left encounters the String and reads everything
after it as a String. It will perform String concatenation.
Output:
We want to add 1015
10 and 15 are printed as if they are String literals.
Strings & Numbers
The plus sign is also used as the addition
operator.
System.out.println(36 + 4 + “ is 36 + 4”);
The numbers will be added together because
they are at the beginning before the String. So
it will perform addition.
Output: 40 is 36 + 4.
Strings and Numbers
You can use parentheses to force addition with
the + sign.
System.out.println(“36 + 5 = “ + (36+5));
Parentheses have highest precedence so it
performs that operation first.
Output: 36 + 5 = 40
What will print?
System.out.println("12" + 3 + 4);
1234
127
System.out.println("12" + (3 + 4));
System.out.println(12 + 3 + 4);
System.out.println(12 + "3" + 4);
System.out.println(12 + 3 + "4");
19
1234
154
Check
Printing String literals with concatenation
What will the following print?
System.out.println(“This will print “ + 3 + 2 + 0);
This will print 320
System.out.println(“This will print “ + (3 + 2 + 0));
This will print 5
System.out.println(3 + 2 + 0 + “ will print”);
System.out.println(“This
will print “ + 2 * 6);
5 will print
This will print 12
public class ConcatenationRules
{
public static void main(String[]args)
{
System.out.println("This will not add the numbers 10 + 15 together " + 10 + 15 );
System.out.println(36 + 4 + " will be the sum of 36 + 4");
System.out.println("This will add 36 + 4 because of the ( ) " + (36+4));
}
}
Output:
This will not add the numbers 10 + 15 together 1015
40 will be the sum of 36 + 4
This will add 36 + 4 because of the ( ) 40
>
Escape sequences Page 60
• Used with Strings to produce a newline, slash
or quotation marks.
\t
\n
\\
\”
tab
will tab 5 spaces
newline
will go to a new line
will print \
will print one slash
will print double quotes
Escape Sequences
//escape characters
public class Escape
{
public static void main(String[]args)
{
System.out.println("A slash n \nis used to go to a new line\n");
System.out.println("A slash quotation mark \"will\" print a double quote");
System.out.println("double slash \\ will print one backslash.");
System.out.println("A slash t twill tab.\n\tName\t\tAge\t\tDOB");
System.out.println("A slash one quotation \'will\' produce single quote.");
}
}
PRIMITIVE DATA TYPES:
Information in program is stored in variables.
Data type is the type of data stored in the variable.
There are 8 Primitive data types in Java.
TYPE
SIZE
RANGE
int
whole numbers
2147483648
2147473647
double
fractional
numbers
±4.94065645841246544E-324;
±1.79769313486231570E+308
boolean
{true, false}
Holds two values: {true, false}
Memory Storage
• In order to reserve space in memory for the
variable, the computer has to know what
type of data it will be.
• Declare = to tell what type of data the
variable will hold and its name
• Initialize = assign the variable a value using
the = sign
Declare is to tell what type of data the variable will hold and its name
• the computer needs to know how much memory to store for that variable
•
int number;
double money;
boolean done;
You cannot use a variable until you declare the type
Initalize is to assign the variable a value using the = sign
number = 4;
money = 7.50;
done = false ;
Can Initialize & Declare at same time
int number = 37;
double money = 28.42;
boolean done = true;
data type with operations
• when you use 2 integers in an operation the
result is an integer
• 20/6 + 3 = 20/6 = 3 + 3 = 6
• When you use a double as one of the
operands then the result is a double
• 20/6.0 + 3 = 20/6.0 = 3.333 + 3 = 6.333
Using variables to store the answer
Storing that information in a variable
• integers can be stored in an int or a double
int a = 20;
int b = 6
int c = 3;
int d;
double d;
d= a/b+c;
20/6
+ 3 =+6.0;
20/6
3 =6
Variables
• A variable is a name for a location in memory
• A variable must be declared by specifying the variable's
name and the type of information that it will hold
data type
variable name
int total;
int count, temp, result;
Multiple variables can be created in one declaration
19
Variables
• A variable can be given an initial value in the
declaration. Called initializing.
int sum = 0;
int base = 32, max = 149;
double amount = 47.52;
boolean done = false;
 When a variable is referenced
in a program, its current value
is used
 See PianoKeys.java
20
public class PianoKeys
{
//---------------------------------------------------------------// Prints the number of keys on a piano.
//---------------------------------------------------------------public static void main (String[] args)
{
int keys = 88;
System.out.println ("A piano has " + keys +
" keys.");
}
}
Assignment
• An assignment statement changes the value of a variable
• The assignment operator is the = sign
int total = 55;
total = 47;
 The expression on the right is evaluated and the result is stored in the
variable on the left
 The value that was in total initially is overwritten
 You can assign only a value to a variable that is consistent with the
variable's declared type could not say total = 47.50 because total is
declared as an int;
 See Geometry.java (page 70)
21
//********************************************************************
// Geometry.java
Author: Lewis/Loftus/Cocking
//
// Demonstrates the use of an assignment statement to change the
// value stored in a variable.
//********************************************************************
public class Geometry
{
//----------------------------------------------------------------// Prints the number of sides of several geometric shapes.
//----------------------------------------------------------------public static void main (String[] args)
{
int sides = 7; // declaration with initialization
System.out.println ("A heptagon has " + sides + " sides.");
sides = 10; // assignment statement
System.out.println ("A decagon has " + sides + " sides.");
sides = 12;
System.out.println ("A dodecagon has " + sides + " sides.");
}
•
}