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SESSION 4 : BUILT-IN
CLASSES IN JAVA
Mahmoud Ali | ACM Shoubra

Contents
 Arrays Class
 Math Class
 Wrapper Classes
 Integer
 Long
 Double
 Float
 Char
 BigInteger Class

Built-in Classes
 Java provide some useful classes in the java.lang
package .
 These classes provide us with some methods and
fields that help us save time and effort in writing
code and repeating it more and more…

Class and Instance Methods
 Instance Method : a method defined for an object.
 Class Method : a method defined for a class.
*an introduction to object oriented programming in java ,5th Edition , C . Thomas WU

Arrays Class
 Class Arrays helps you avoid reinventing the wheel
by providing static methods for common array
manipulations
 Methods Include
 sort(array) : Arranges array elements into increasing
order.
 binarySearch(array , element) : Determines whether an
array contains a specific value and, if so, returns where the
value is located.
 equal(array) : Compares arrays.
 fill(array , element) : Places Values into an array.
 toString() : Converts array to String.

Arrays Class (cont.)
 We can copy arrays using copyof method of the
class Arrays Or using class System’s static
arraycopy method.
 To use Arrays Class we import it by
import java.util.Arrays ;
 To Access Class methods we use the (.) operator.
 Ex:-
 Arrays.sort(array);

Math Class
 Using only the arithmetic operators to express numerical
computations is very limiting. Many computations
require the use of mathematical functions.
 For example , Expressing The Following Formula
 The Math class in the java.lang package contains class
methods for commonly used mathematical functions.
 To use Math Class we import it by :
 import java.lang.Math;

Math Class (cont.)
 Math Class Methods include
 abs(a) : Returns the absolute value of a.
 ceil(a) : Returns the smallest whole number greater than a.
 floor(a) : Returns the largest whole number less than a.
 max(a , b) : Returns the larger of a and b.
 min(a , b) : Returns the smaller of a and b.
 pow(a , b) : Returns the number a raised to power b.
 random() : Generates a random number less than or
equal to 0.0 and less than 1.0 .
 sqrt(a) : returns the square root of a.

Math Class (cont.)
 toDegrees() : Converts the given angle in radians to
degrees.
 toRadians() : Reverse of toDegrees.
 Trigonometric Functions
 sin(a)
 cos(a)
 tan(a)
 All trigonometric functions are computed in radians.
 Arc Trigonometric Functions
 asin(a)
 acos(a)
 atan(a)

 Let’s Code the Formula :

Wrapper Classes
 Each of Java's eight primitive data types has a
class dedicated to it.
 These are known as wrapper classes, because they
"wrap" the primitive data type into an object of
that class.
 there is an Integer class that holds an int variable.

Wrapper Classes(cont.)
 Wrapper Classes have Objects Defined as Follows :
 Integer
 Integer x = new Integer(value);
 Long
 Long x = new Long(value);
 Double
 Double x = new Double (value);
 Float
 Float x = new Float(value);
 Char
 Character x = new Character(value);

 Wrapper Classes have a lot of methods in common :
 toString() Method :
 For Example :
 String s = Integer.toString(5);
 String s = Character.toString(‘a’);
 parse Method : Converts String to an Int , float, double ,..
 Int x = Integer.parseInt(“1234”);
 double x = Double.parseDouble(“12.1545”);
 Minimum and Maximum Values of a Primitive type
 Int min = Integer.MIN_VALUE; //min =-2147483648
 Int max = Integer.MAX_VALUE; // max = 2147483647
 float maxv = Float.MAX_VALUE; //maxv = 3.4028235E38

 Converting between primitive data types :
 doubleValue() returns the value of this type as an double.
 floatValue() returns the value of this type as a float.
 intValue() returns the value of this type as an int.
 longValue() returns the value of this type as a long.
 For Example
 int x = 15;
 float y = x.floatValue();

 Converting to another number system :
 toBinaryString(a) : Converts a into binary string.
 toHexString(a) : Converts a into hexadecimal string.
 toOctalString(a) : Converts a into octal String.
 For Example :
 String s = Integer.toBinaryString(10);

BigInteger Class
 The java.math.BigInteger class provides operations
analogues to all of Java's primitive integer operators
and for all relevant methods from java.lang.Math.
 BigInteger class help us to deal with very large
Integers.
 To Declare A BigInteger We Use :
 BigInteger num = BigInteger.valueof(long number);

BigInteger Class(cont.)
 BigInteger Fields Include :
 BigInteger.ONE : The BigInteger constant one.
 BigInteger.ZERO : The BigInteger constant zero.
 BigInteger.TEN : The BigInteger constant ten.
 BigInteger Methods Include :
 abs() : returns a BigInteger whose value is the absolute
value of this BigInteger.
 add(val) : returns a BigInteger whose value is (this + val).
 subtract(val) : returns a BigInteger whose value is (this - val).
 multiply(val) : returns a BigInteger whose value is (this*val).
 divide(val): returns a BigInteger whose value is (this / val)

 pow(int ex) : returns a BigInteger whose value is thisex .
 nextProbablePrime() : returns the first integer greater than
this BigInteger that is probably prime.
 isProbablePrime() : returns true if this BigInteger is probably
prime, false otherwise .
 intValue() : converts this BigInteger to an int.
 longValue() : converts this BigInteger to a Long.
 floatValue() : converts this BigInteger to a float.
 doubleValue() : converts this BigInteger to a double.
 toString() : returns the decimal String representation of this
BigInteger.
 negate() : returns a BigInteger whose value is (-this).

 Example(http://www.spoj.com/problems/FCTRL2/)
 You are asked to calculate factorials of some small
positive integers where 1<=n<=100

References
 Java How To Program ,early objects 9th edition ,
Deitel.
 an introduction to object oriented programming in
java ,5th Edition , C . Thomas WU .
 Java An Introduction to Problem Solving and
Programming , 6th Edition ,Walter Savitch
 TutorialsPoint.com

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Built-in Classes in JAVA

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