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Introduction to Java
Hello World Program
Variables and Data types
More about data types
Displaying text using print and println
Displaying text using printf
Java Comments
Naming conventions for Identifiers
Mathematical operations in Java
Taking input from the user

Classes and Objects
Introduction to object oriented programming
The constituents of a Class
Creating objects and calling methods
Get and Set Methods
Default constructor provided by the compiler
Access Specfiers
Scope and lifetime of Variables
Call by value and Call by Reference

A few more topics
Casting
Class as a reference data type
Constants or literals
Final variables
Increment and decrement operators
Manipulating Strings
Operators
Overloading constructors and methods
Static methods and variables
The Java API
The Math class
this keyword
Wrapper classes

Control Structures
Control Statements
Repetition statements
Nested loops
Formulating algorithms
Branching Statements

Arrays
Arrays introduction
Processing arrays using 1oops
Searching and sorting arrays
Array of objects
Multi dimensional arrays
Taking input as command line arguments
Using ellipsis to accept variable number of arguments

Inheritance
Inheritance introduction
Relation between a super class and sub class
Final classes and methods
The protected access specifier
Class Object

Polymorphism
Introduction
Interfaces
Packages
Abstract classes and methods

Exception handling
Exception handling introduction
Exception hierarchy
Nested try catch blocks
Throwing exceptions


Displaying Information using print() and println() Methods

We have already seen how the println() method is used to print text on the screen. In addition to the println() method, we have the print() and the format() methods which are used for displaying data. The print() method is similar to the println() statement while the format() method is something different.

Difference between print() and println()

The only difference between the print() and println() methods is that the println() statement positions the cursor onto the next line after printing the desired text while the print() method leaves the cursor on the same line. The difference is evident when we print text using more than a single statement. The following statements use the print() method.

System.out.print("Hello ");
System.out.print("World ");

The output of these statements would be:

Hello World

After printing the word 'Hello', the cursor remained on the same line. That is why 'World' was also displayed on the same line. If we use the println() statement, the output would be different.

System.out.println("Hello ");
System.out.println("World ");

The output would be

Hello
World

After printing the word 'Hello', the cursor moved to the next line. That is why the word 'World' was printed on a new line.

Concatenation using + operator

We can use the concatenation operator + to join two or more Strings and print them. To print the value of a variable, we simply state it within the parentheses. Look at the following code for example:

int a=1;
String s = "World";
System.out.println(a+" "+"Hello "+s+"!");

The output would be

1 Hello World!

The expression within the parentheses is evaluated from left to right and particular care has to be taken when including variables that store integers, real numbers and characters.

Including integers and real numbers in print statements

The order in which these variables that store integers and real numbers occur along with the Strings can decide whether the integers would be printed directly or if they would be added together with integers and then printed. When a String is added to any other data type, the resultant value is a String. The other variable is also converted to a String and then concatenated. However, when two integers are operated with a + sign, the + acts as an addition operator and not a concatenation operator. The variables are considered as int's and not Strings. Parentheses may be used just as in maths to alter the order in which evaluation is performed. If the expression within the println() or print() method contains parentheses, then the value within the parentheses is evaluated first. Consider the following example:

int a = 3;
int b = 4;
System.out.println( a + b );
System.out.println( "3" + "4" );
System.out.println( "" + a + b );
System.out.println( 3 + 4 + a + " " + b + a );
System.out.println( "Result: " + a + b );
System.out.println( "Result: " + ( a + b ) );

The output would be

7
34
34
10 43
Result: 34
Result: 7


Expressions within the parentheses are evaluated from left to right. In the first println() statement, both a and b are integers. Hence, they are added together and the result 7 is displayed. In the second statement, the Strings "3" and "4" were joined by a + sign. It is to be noted that, here 3 and 4 are Strings and not integers. In the third line, the empty String, represented by the opening and closing quotes is added to the integer 3. Since a String was added to the integer 3, the resultant value is a String "3" and not the integer 3. Next this String is added to the integer 4. Therefore, the integer 4 is converted to the String "4" and concatenated with the String "3" to give the String "34". In the fourth statement, starting from the left as usual, we have the integers 3, 4 and a connected with a + sign. Hence, they are all added to give 10, an integer. Now this integer is added to a String " " giving the String "10 "and continuing in similar manner, we get the result "10 43". In a similar way, the next statement gives the answer "Result: 34". In the last statement, parentheses have been used to alter the order in which evaluation is performed. First, the expression within the parentheses is evaluated. Hence, a + b is evaluated to give an integer 7, which is concatenated with the String "Result: " to give the final String "Result: 7".

Printing characters

Whenever a char variable is passed as a parameter to the print() or println() methods, the graphic representation is printed and not the numeric value. It does matter whether we have initialised the char with a number or with a graphic symbol.

char a=65;
char b='A';
System.out.println(a);
System.out.println(b);

The output would be

A
A

If we want the numeric representation to be printed, we need to cast the variable into one of the four integer types.

System.out.println((int)a);

The output would be

65

When an integer is added to a char, the char is implicitly casted to an integer.

System.out.println(b+1);

The output would be

66

Using escape sequences to print new lines and tabs

We can print new lines and tabs using escape sequences. Escape sequences are a combination of a backslash character '\' followed by one or more letters. To print a new line, we use the escape sequence '\n' and to print a tab ( a group of spaces), we use the escape sequence '\t'.

Following examples shows the use of escape sequences.

String str="Hello World!"; System.out.println (str + "\nA new line+"\t" + "Tab"+"\n" + "A new line");

The output would be

Hello World!
A new line    Tab
A new line

Note that the escape characters can also be used in Strings that would be stored in a variable. The escape sequences are single characters which can be stored in a char variable. However, they are generally taken as Strings in order to avoid them being converted to integers due to logical errors. Look at the following code where a logical error exists. The intended output is the numbers 3,4 and 7 on different lines but the actual output was something different since the escape sequence '\n' was converted into its numeric value 10.

int a=3,b=4,c=7;
System.out.println(a+'\n'+ b+'\n'+ c);

The output is

34

The reason is that the char '\n' was converted into its numeric value 10. The logical errors could have been avoided if the escape sequences were considered as Strings and not chars.

System.out.println(a+"\n"+b+"\n"+c);

The output now would be

3
4
7

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