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Quick introduction to Java Programming language - Part 1

Chapters

Working with Characters and Strings

To work with characters, we normally use char of primitive data types. Char is used to store the single letter, it also supports for array.

Example:

char grade='b'; // an array of chars

char[] alphabetArray={'d','a','b','c','h'};

In some situations we need to use objects instead of primitive data types. To achieve this, Java has wrapper class Character for primitive type char.

We can create anobjectof Character:

Character ch=new Character('Z');

The Character class provides many useful class static methods for characters operation.

The Java compiler has the capability to create a Character object for under some circumstances. For example: if a primitive char is argument of a method which accepts an object, the java compiler converts automatically the char to a Character. This process is called unboxing.

* Information below is collected from oracle.com docs for Java SE

Escape Sequences

A character preceded by a backslash (\) is an escape sequence and has special meaning to the compiler. The following table shows the Java escape sequences:


Escape Sequence	Description
`\t`	Insert a tab in the text at this point.
`\b`	Insert a backspace in the text at this point.
`\n`	Insert a newline in the text at this point.
`\r`	Insert a carriage return in the text at this point.
`\f`	Insert a formfeed in the text at this point.
`\'`	Insert a single quote character in the text at this point.
`\"`	Insert a double quote character in the text at this point.
`\\`	Insert a backslash character in the text at this point.

The compiler will interpret an escape sequence correctly when encountered in a print statement.

Here is an example to print a string with escape sequence characters

I said "Hi!".

Above string if you like to use in a program should be used as

System.out.println("I said \"Hi!\".");

Character Methods:

Here is the list of the important instance methods that all the subclasses of the Character class implement:

Methods	Description	Parameter	Return Value	Syntax
toUpperCase()	To convert the given char into upper case form	Primitive character type	Returns the uppercase form of the given char value.	char toUpperCase(char name) Example: System.out.println(Character.toUpperCase('l'));//returns L System.out.println(Character.toUpperCase('A'));//returns A
isUpperCase()	To check the given char value is in Upper case form or not.	Primitive character type	Returns Boolean value True/False	booleanisUpperCase(char city) Example: System.out.println(Character.isUpperCase('a'));//returns False System.out.println(Character.isUpperCase('A'));//returns True
toLowerCase()	To convert the given char into Lower case form	Primitive character type	Returns the Lowercase form of the given char value.	chartoLowerCase(charcityname) Example: System.out.println(Character.toLowerCase('T')); //returns t System.out.println(Character.toLowerCase('r')); //returns r
isLowerCase()	To check the given char value is in Lower case form or not.	Primitive character type	Returns Boolean value True/False	booleanisLowerCase(char city) Example: System.out.println(Character.isUpperCase('a'));//returns True System.out.println(Character.isUpperCase('A'));//returns False
isLetter()	To check the given char value is a letter or not.	Primitive character type	Returns Boolean value True/False	boolean isLetter(char a) Example: System.out.println(Character.isLetter('6')); //returns False System.out.println(Character.isLetter('u')); //returns True
toString()	Returns a String object representing the given character,one-character string.	Primitive character type	Returns String object	StringtoString(charch) Example: System.out.println(Character.toString('A'));//returns A System.out.println(Character.toString('a'));//returns a
isWhitespace()	The method checks the given char is a white space, which includes space, new line or tab	Primitive character type	Returns Boolean value True/False	boolean isWhitespace(char name) Example: System.out.println(Character.isWhitespace(' ')); //returns True System.out.println(Character.isWhitespace('a'));//returns False
isDigit()	To checks the given char is a digit or not.	Primitive character type	Returns Boolean value True/False	boolean isDigit(char city) Example: System.out.println(Character.isDigit('8')); //returns True System.out.println(Character.isDigit('a')); //returns False

String Class

Strings are a group of characters. In the Java language, strings are objects.Javaprovides the String class for creation and manipulation of strings

Creating Strings:

To create a string:

String msg="Java World!”;

Whenever there is a string literal in java code, the java compiler creates a String object with its value in this case, "Java World!'.

Similar to other objects, String object can be created by using new Keyword. The String class provides eleven constructors to give value of string from different source or array of characters.

public class DemoString{
   public static void main(String args[]){
		char[]ArrayExample = {‘J’,’A’,’V’,’A’};
		StringJavaString = new String(ArrayExample);  
		System.out.println(JavaString);
   }  
}

Output: JAVA

Some of String Methods:

Method Name	Example
char charAt(int index) Returns character at specified index.	public class Example { public static void main(String args[]) { String temp = "Java"; char result = s.charAt(3); System.out.println(result); } } OutPut : a
intcompareTo(Object o) Compares two string objects. Return 0 if they are equal	public class Example { public static void main(String args[]) { String temp = "Java"; String temp1 = "Java"; int result = temp.compareTo( temp1 ); System.out.println(result); } } Output : 0
String concat(String str) Concatenates specified string to end of string.	public class Example { public static void main(String args[]) { String s = "JAVA"; s = s.concat("is good"); System.out.println(s); } } output: JAVA is good
int length() Returns length of string.	public class Example{ public static void main(String args[]){ String Str = new String("JAVA"); System.out.println(Str.length()); } } OUTPUT: 4
char[] toCharArray() Converts string to new character array	public class Example{ public static void main(String args[]){ String St = new String("JAVA"); System.out.println(St.toCharArray() ); } } OUTPUT: JAVA
String trim() Returns copy of string removing whitespace leading and trailing	public class Example{ public static void main(String args[]){ String Str = new String(" JAVA is good "); str = str.trim(); System.out.println(str); } } Output : JAVA is good
String toUpperCase() Converts all characters in String to upper case	public class Example{ public static void main(String args[]){ String Str = new String("java"); str = str.toUpperCase(); System.out.println(str); } } Output : JAVA
String toLowerCase() Converts all characters in String to lower case	public class Example{ public static void main(String args[]){ String Str = new String("JAVA"); str = str.toLowerCase(); System.out.println(str); } } Output : java
String replace(char oldChar, char newChar) Returns a new string by replacing all occurrences of oldChar in string with newChar.	public class Example{ public static void main(String args[]){ String Str = new String("JAVA"); System.out.println(Str.replace('J', 'C')); } } OUTPUT:CAVA
String[] split(String regex) Splits string around matches of given regular expression.	public class Example{ public static void main(String args[]){ String Str = new String("JAVA is good"); for (String retval: Str.split("-", 2)){ System.out.println(retval); } } } Output : `JAVA is` `- good`

Description

This tutorial is targetted for beginers seeking a quick get on with guide on Java programming language. 3 parts include

Java basics
Object oriented programming
Advance concepts

Each part is subdivided in multiple chapters.

Java basics has the following chapters

Introduction
Environment Setup
Basic Syntax
Objects and Classes
Basic Data Types
Variable Types
Modifier Types
Basic Operators
Loops
Decision Making
Numbers Class
Character and String Class
Arrays
Date and Time
Regular Expression
Methods
Streams, Files and I/O
Exceptions Handling

Thanks for reading and as always, your feedback is very important to us. Let us know how we can improve and if you found any issues with this write up, send us a correction.

Audience

Beginners or students seeking a refresher on Java language

Author: Subject Coach
Added on: 9th Mar 2015

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