Chapter 4

Mathematical Functions, Characters, and Strings

Mathematical Functions

Java provides many useful methods in the Math class for performing common mathematical functions.

The Math Class

Class methods

Trigonometric Methods
Exponent Methods
Rounding Methods
min, max, abs, and random Methods

Trigonometric Methods


						Examples:
                        Math.sin(0) returns 0.0 
                        Math.sin(Math.PI / 6) returns 0.5 
                        Math.sin(Math.PI / 2) returns 1.0
                        Math.cos(0) returns 1.0
                        Math.cos(Math.PI / 6) returns 0.866 
                        Math.cos(Math.PI / 2) returns 0

Exponent Methods

Rounding Methods

double ceil(double x) x rounded up to its nearest integer. This integer is returned as a double value.
double floor(double x) x is rounded down to its nearest integer. This integer is returned as a double value.
double rint(double x) x is rounded to its nearest integer. If x is equally close to two integers, the even one is returned as a double.
int round(float x) Return (int)Math.floor(x+0.5).
long round(double x) Return (long)Math.floor(x+0.5).

Rounding Methods Examples

min, max, and abs

max(a, b)and min(a, b) Returns the maximum or minimum of two parameters.
abs(a) Returns the absolute value of the parameter.
random() Returns a random double value in the range (0.0, 1.0).

The random method

Generates a random double value greater than or equal to 0.0 and less than 1.0 (0 <= Math.random() < 1.0)



                        Returns a random integer between 0 and 9
						(int)(Math.random()*10)  
                        -------------------------------------------------- 
                        Returns a random integer between 50 and 99
                        50 + (int)(Math.random() * 50 ) 
                        -------------------------------------------------- 
                        a + Math.random() * b 
                        Returns a random number between a and a+b, excluding a+b.

Math Examples

Math code

Character Data Type

Character may contain a single field whose type is char The char data type is a primitive data type and is widely used for handling text and characters in Java programs.

char letter ='A' (ASCII)

char numChar ='4' (ASCII)

char letter='\u0041' (Unicode)

char numchar='\u0043' (Unicode)

Character Examples


                        public class CharInString {
                            public static void main(String[] args) {
                                String message = "Hello, World!";
                                char firstChar = message.charAt(0); // Get the first character
                                char lastChar = message.charAt(message.length() - 1); // Get the last character
                                System.out.println("First Character: " + firstChar);
                                System.out.println("Last Character: " + lastChar);
                            }
                        }

ASCII Table

Character Data Types

Sample code on Github character code

Special String Characters



                       String txt="We are the so-called "Vikings" from the north";

Special Character	Display
\'	Single quotation mark
\"	Double quotation mark
\\	Backslash
\t	Tab
\r or \n	Carriage return

Special String Characters

Comparing and Testing Characters

Character Method example

                        
                            char ch='A';
                            System.out.println(  Character.isDigit(ch));
                            System.out.println(Character.isAlphabetic(ch));
                            System.out.println(Character.isLowerCase(ch));

The String Type

In Java, the String type is used to represent a sequence of characters. It is one of the most commonly used data types for handling text and is part of the java.lang package. Strings in Java are immutable , meaning once a String object is created, its value cannot be changed. Instead, any operation that modifies a String creates a new String object.

What is String?

String is actually a predefined class in the Java library just like the System class and Scanner class.

Any Java class can be used as a reference type for a variable.

It is known as a reference type.

The String type is not a primitive type.

String Examples

Sample code on Github string code

String Immutability

Strings in Java are immutable. This means that once a String object is created, its value cannot be changed.


                        String str = "Hello";
                        str = str + " World!"; // Creates a new String object
                        System.out.println(str); // Output: Hello World!

In the above example, the original string "Hello" is not modified. Instead, a new string "Hello World!" is created

Immutable Example

Immutable code

How String store value?

String Equality?

Interned String

String Interning in Java is a process where identical strings are searched in the string pool and if they are present, the same memory is shared with other strings having the same value.

The intern() method creates an exact copy of a String that is present in the heap memory and stores it in the String constant pool.

Note - intern() method is used to store the strings that are in the heap in the string constant pool if they are not already present.

Interned String

Interned Example

Interned code

String Comparision

Best Pratices

Use equals() not == to compare two strings
== operator compares memory location
While equals() method compare the content stored in two objects
s1.equal(s2)

Converting Strings


				
                        System.out.println("welcome".toLowerCase());//return a new string welcome.
                        System.out.println("welcome".toUpperCase()) ;//return a new string WELCOME.
                        System.out.println("   Welcome ".trim()) ;//returns a new string , Welcome

String Concatenation


				
                        String s1= "IS147";
                        String s2="JAVA";
                        String s3=s1.concat(s2);
                        String s4=s1+s2;
                        //Three strings are concatenated
                        String message="Welcome" + " to" + "java";
                        //String chapter is concatenated with number 2
                        String s= "Chapter" + 2; // s becomes Chapter2
                        //String Supplement is concatenated with character b
                        String s5= "Supplement" + 'B'; //s1 becomes SupplementB
                        System.out.println(message);
                        System.out.println("Using concat " +s3);
                        System.out.printf("Using + symbol with number %s %n" ,s4);
                        System.out.printf("Using char + %s %n" ,s);

Immutable Example

String objects are immutable. Immutable simply means unmodifiable or unchangeable.
Once String object is created its data or state can't be changed but a new String object is created.

Immutable code

String Immutable

String Concatenation


				
                       String s3=s1.concat(s2); or String s3=s1+s2;
                       //Three strings are concatenated
                       String message="Welcome" + " to" + "java";

                       //String chapter is concatenated with number 2
                       String s "Chapter" + 2; // s becomes Chapter2

                       //String Supplement is concatenated with character b
                       String s1= "Supplement" + 'B'; //s1 becomes SupplementB

THE END

Questions

Group Project

- Lab 3