Download 1.2 Built-in Data Types

Integers
1.2 Built-in Data Types
int data type. Useful for expressing algorithms.
Data type
* A set of values.
* A set of methods or operations that can be applied to the data.
We learned integer and floating point data types in Java:
int, byte, short, long, double, float
There are 2 more built-in primitive types – char and boolean.
There is another built-in type – String.
Java also lets you construct your own data types.
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Floating-Point Numbers
Math Library
double data type. Useful in scientific applications.
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Type Conversion
Basics of Programming
Type conversion. Convert from one type of data to another.
Automatic: promotion.
Explicit: cast.
Definitions.
!!
!!
Some examples:
Expression
type
value
Trace.
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Random Integer
Quadratic Equation
Ex. Generate a pseudo-random number between 0 and N-1.
Ex. Solve quadratic equation x2 + bx + c = 0.
public class RandomInt {
public static void main(String[] args) {
int N = Integer.parseInt(args[0]);
double r = Math.random();
String to int (method)
int n = (int) (r * N);
// parse coefficients from command-line
double b = Double.parseDouble(args[0]);
double c = Double.parseDouble(args[1]);
double between 0.0 and 1.0
// calculate roots
double discriminant = b*b - 4.0*c;
double d = Math.sqrt(discriminant);
double root1 = (-b + d) / 2.0;
double root2 = (-b - d) / 2.0;
System.out.println("random integer is " + n);
}
% java
random
% java
random
% java
random
RandomInt 6
integer is 3
RandomInt 6
integer is 0
RandomInt 10000
integer is 3184
"b ± b 2 " 4 c
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public class Quadratic {
!
public static void main(String[] args) {
double to int (cast) int to double (automatic)
}
roots =
int to String (automatic)
}
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}
// print them out
System.out.println(root1);
System.out.println(root2);
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Built-in Data Types
Text
Data type. A set of values and operations defined on those values.
type
set of values
literal values
operations
char
characters
'A'
'@'
compare
String
sequences of
characters
"Hello World"
"CS is fun"
concatenate
int
integers
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12345
add, subtract,
multiply, divide
double
floating point
numbers
3.1415
6.022e23
add, subtract,
multiply, divide
boolean
truth values
true
false
and, or, not
Char data type. A char is a alphanumeric character or a symbol.
typical literals: ‘a’, ‘A’, ‘%’, ‘\n’, …
Operation: Usually not direction operation. Try (char)(’a’ + 2).
String data type. Useful for program input and output.
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Subdivisions of a Ruler
String
!!
public class Ruler {
public static void main(String[] args) {
String ruler1 = "1";
String ruler2 = ruler1 + " 2 " + ruler1;
String ruler3 = ruler2 + " 3 " + ruler2;
String ruler4 = ruler3 + " 4 " + ruler3;
System.out.println(ruler4);
}
}
Convert a String to int or double numbers.
"1"
"1 2 1"
"1 2 1 3 1 2 1"
!!
string concatenation
Primitive types are automatically promoted to String when using “+”
operator.
% java Ruler
1 2 1 3 1 2 1 4 1 2 1 3 1 2 1
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Booleans
Truth Table
Prove: a&&b and !(!a || !b) are identical
boolean data type. Useful to control logic and flow of a program.
a
b
a && b
!(!a || !b)
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Comparisons
Leap Year
Comparisons. Take operands of one type and produce an operand of
type boolean.
Q. Is a given year a leap year?
A. Yes if either (i) divisible by 400 or (ii) divisible by 4 but not 100.
public class LeapYear {
public static void main(String[] args) {
int year = Integer.parseInt(args[0]);
boolean isLeapYear;
// divisible by 4 but not 100
isLeapYear = (year % 4 == 0) && (year % 100 != 0);
// or divisible by 400
isLeapYear = isLeapYear || (year % 400 == 0);
System.out.println(isLeapYear);
}
}
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% java LeapYear 2004
true
% java LeapYear 1900
false
% java LeapYear 2000
true
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