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Programming Language
Foundation
BY Dr. BABAOUSMAIL HASSEN
LECTURER AT BINJIANG COLLEGE OF NUIST

Chapter 4
Mathematical Functions,
Characters, and Strings
Continue…

Case Study:
Computing Angles of a Triangle
Write a program that prompts the user to enter the x- and y-
coordinates of the three corner points in a triangle and then
displays the triangle’s angles.
3
A
B
C
a
b
c
A = acos((a * a - b * b - c * c) / (-2 * b * c))
B = acos((b * b - a * a - c * c) / (-2 * a * c))
C = acos((c * c - b * b - a * a) / (-2 * a * b))
x1, y1
x2, y2
x3, y3

Character Data Type
In addition to processing numeric values, you can process
characters in Java.
The character data type, char, is used to represent a single
character.
A character literal is enclosed in single quotation marks.
Consider the following code:
char letter = 'A';
char numChar = '4';
◦ The first statement assigns character A to the char variable letter.
◦ The second assigns digit character 4 to the char variable numChar.
4

Character Data Type,
Computers use binary numbers internally. A character is stored in a computer as a
sequence of 0s and 1s.
Mapping a character to its binary representation is called encoding. There are
different ways to encode a character.
◦ Unicode
◦ ASCII code
Java supports Unicode, which was originally designed as a 16-bit character
encoding. A 16-bit Unicode takes two bytes, preceded by u, expressed in four
hexadecimal digits that run from u0000 to uFFFF.
Most computers use ASCII (American Standard Code for Information Interchange),
an 8-bit encoding.
Unicode includes ASCII code, with u0000 to u007F corresponding to the 128
ASCII characters.
5

Character Data Type,
NOTE: The increment and decrement operators can also be
used on char variables to get the next or preceding Unicode
character.
For example, the following statements display character b.
◦ char ch = 'a‘;
◦ System.out.println(++ch);
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char letter = 'A'; (ASCII)
char numChar = '4'; (ASCII)
char letter = 'u0041'; (Unicode)
char numChar = 'u0034'; (Unicode)
Four
hexadecimal
digits.

Unicode Format
Unicode takes two bytes, preceded by u, expressed in four
hexadecimal numbers that run from 'u0000' to 'uFFFF'.
Unicode can represent 65534 characters.
7
Unicode u03b1 u03b2 u03b3 for three Greek
letters

ASCII Character Set,
ASCII Character Set is a subset of the Unicode from
u0000 to u007F
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ASCII Code for Commonly Used Characters
9
Characters Code Value in Decimal Unicode Value
'0' to '9' 48 to 57 u0030 to u0039
'A' to 'Z' 65 to 90 u0041 to u005A
'a' to 'z' 97 to 122 u0061 to u007A

Escape Sequences
for Special Characters
10

A char can be cast into any numeric type, and vice versa.
◦ When an integer is cast into a char, only its lower 16 bits of data are used; the other
part is ignored.
◦ When a floating-point value is cast into a char, the floating-point value is first cast
into an int, which is then cast into a char.
◦ When a char is cast into a numeric type, the character’s Unicode is cast into the
specified numeric type.
11
Casting between char and
Numeric Types

Casting between char and Numeric
Types, cont.
Implicit casting can be used if the result of a casting fits into
the target variable. Otherwise, explicit casting must be used.
For example,
12
√
√
×
√

Comparing and Testing Characters
Two characters can be compared using the relational
operators just like comparing two numbers. This is done by
comparing the Unicodes of the two characters.
For example,
if (ch >= 'A'&& ch <= 'Z')
System.out.println(ch + " is an uppercase letter");
else if (ch >= 'a' && ch <= 'z')
System.out.println(ch + " is a lowercase letter");
else if (ch >= '0' && ch <= '9')
System.out.println(ch + " is a numeric character");
13

Methods in the Character Class
For convenience, Java provides the following methods in the
Character class for testing characters.
14
Method Description
isDigit(ch) Returns true if the specified character is a digit.
isLetter(ch) Returns true if the specified character is a letter.
isLetterOfDigit(ch) Returns true if the specified character is a letter or digit.
isLowerCase(ch) Returns true if the specified character is a lowercase letter.
isUpperCase(ch) Returns true if the specified character is an uppercase letter.
toLowerCase(ch) Returns the lowercase of the specified character.
toUpperCase(ch) Returns the uppercase of the specified character.

The String Type
The char type only represents one character. To represent a string of
characters, use the data type called String.
For example,
String message = "Welcome to Java ";
The String type is not a primitive type. It is known as a reference
type. Any Java class can be used as a reference type for a variable.
Reference data types will be thoroughly discussed in Chapter 9.
For the time being, you just need to know
◦ how to declare a String variable,
◦ how to assign a string to the variable,
◦ how to concatenate strings,
◦ to perform simple operations for strings.
15

Simple Methods for String Objects
16
Method Description
Returns the number of characters in this string.
Returns the character at the specified index from this string.
Returns a new string that concatenates this string with string s1.
Returns a new string with all letters in uppercase.
Returns a new string with all letters in lowercase.
Returns a new string with whitespace characters trimmed on both sides.
length()
charAt(index)
concat(s1)
toUpperCase()
toLowerCase()
trim()

Simple Methods for String Objects
Strings are objects in Java. The methods in the preceding table can only be invoked
from a specific string instance. For this reason, these methods are called instance
methods.
The syntax to invoke an instance method is
referenceVariable.methodName(arguments)
 A non-instance method is called a static method. A static method can be invoked
without using an object.
 The syntax to invoke a static method can be
ClassName.methodName(arguments)
 All the methods defined in the Math class are static methods. They are not tied to
a specific object instance. For example, the pow method in the Math class can be
invoked using.
Math.pow(2, 2.5)
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Getting String Length
String message = "Welcome to Java";
System.out.println("The length of " + message +
" is “ + message.length( ));
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Getting Characters from a String
String message = "Welcome to Java";
System.out.println("The first character in
message is “ + message.charAt(0));
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