Basic Java Chapter 4

Simple Input/Output

Chapter Objectives Upon completion of this chapter, you will know

 Simple command to input character  Simple command to input string  Simple output commands  How to convert string to integer  How to convert string to real

Simple Input Command A program that accepts values at run time is interactive because it exchanges communications, or interacts with the user. In order to provide values during the execution of a program requires input, and the form of input that is used is keyboard entry from the user. Character Input Command In Java programming language, the characters are read from the keyboard by calling the System.in.read() method. This is one of Java’s console functions. This method accepts input from the keyboard. The in object has access to the method named read() that retrieves data from the keyboard.

public class CharacterInput { public static void main( String[] args ) throws Exception { char charInput; System.out.print( "Enter a character: " ); charInput = (char) System.in.read(); System.in.read();System.in.read(); //absorbs the enter key System.out.println( "\n The character entere is: " + charInput ); } }

String Input Command In java programming language, in order to allow a user to enter a string from the keyboard, the InputStreamReader() is required to read characters from the standard input, it converts the raw bytes into Unicode characters. Besides, the BufferedReader() is also used for it provides the readLine() method which allows the program to read from standard input line at a time. import java.io.*; public class StringInput { public static void main( String[] args ) throws Exception { BufferedReader input = new BufferedReader( new InputStreamReader( System.in ) ); String strStudentName; System.out.print( "Enter student name: " ); strStudentName = input.readLine(); System.out.println( "Your Name is: " + strStudentName ); } }

The example show the use of the readLine() method to allow the user to enter a string. Java implements I/O operations through streams. The streams are represented by two abstract classes, which include the InputStream and OutputStream. These classes are found in java.io package. Thus, at the beginning of the program, the java.io package is imported into the program. Simple Output Command In Java Programming language, the terminal window is used as the standard output. System.out is PrintStream object that allows us to write to “standard output”. There are two methods used in Java programming that allows the user to display the input that had been entered to the screen, which include the print() and println() method. The difference between the two methods was mentioned in the earlier chapters. Converting String to Integers If a String contains all numbers, we can convert it from String to a number so that we can use it for arithmetic calculation, or to use like any other number. To convert a String to an integer, we can use the Integer class, which is part of the java.lang package, and is imported into programs we write automatically. A method of the Integer class, which is parseInt(), is used to convert String to integer. It takes a String argument and returns its integer value.

import java.io.*; public class IntegerInput { public static void main( String[] args ) throws Exception { BufferedReader input = new BufferedReader( new InputStreamReader( System.in ) ); String numberOfStudents; int studNum; System.out.print( "Enter a number of students: " ); numberOfStudents = input.readLine(); studNum = Integer.parseInt( numberOfStudents ); System.out.println( "Total is " + studNum ); } }

Conversion String to Real We can also convert a String to a double by using the Double class, which is also a part of java.lang package. A method of the Double class, which is parseDouble(); is used to convert the String to double. It takes the String argument and returns its double value. import java.io.*; public class DoubleInput { public static void main( String[] args ) throws Exception { BufferedReader input = new BufferedReader( new InputStreamReader( System.in ) ); String feePayment; double payment; System.out.print( "Enter fees paid: " ); feePayment = input.readLine(); payment = Double.parseDouble( feePayment ); System.out.println( "Total is " + payment ); }

Programming Exercise

Write a program which allows the user to enter his name, age and height. Use Output statement to display the information that he had entered. You should use the correct method to convert the age to integer and height to real number before displaying the information.

Write a program which allows the user to enter two number, multiply and the displays the result on the screen.