Input/Output Statements

Output Statements in Java

Java provides several methods to display output to the console. These methods are part of the System.out object.

1. System.out.print()

Prints text without adding a new line at the end. The cursor remains on the same line.

System.out.print("Hello ");
System.out.print("World");
// Output: Hello World
                

2. System.out.println()

Prints text and moves cursor to the next line. This is the most commonly used output method.

System.out.println("Hello");
System.out.println("World");
// Output: 
// Hello
// World
                

3. System.out.printf()

Provides formatted output using format specifiers. Useful for precise control over output formatting.

String name = "Alice";
int age = 25;
double marks = 85.5;

System.out.printf("Name: %s, Age: %d, Marks: %.2f%n", name, age, marks);
// Output: Name: Alice, Age: 25, Marks: 85.50
                

Input Statements in Java

Java provides various ways to read input from the user. The most common approach is using the Scanner class.

Why Scanner Class?

Simple and easy to use
Supports various data types
Part of Java's standard library (java.util package)
Provides methods for different input types

Using Scanner Class

The Scanner class is used to get user input from various sources like keyboard, files, etc.

Basic Steps:

Import the Scanner class
Create Scanner object
Use appropriate method to read input
Close the Scanner object

import java.util.Scanner;

public class InputExample {
    public static void main(String[] args) {
        // Step 1: Create Scanner object
        Scanner sc = new Scanner(System.in);
        
        // Step 2: Read different types of input
        System.out.print("Enter your name: ");
        String name = sc.nextLine();
        
        System.out.print("Enter your age: ");
        int age = sc.nextInt();
        
        System.out.print("Enter your height (in cm): ");
        double height = sc.nextDouble();
        
        // Step 3: Display the input
        System.out.println("Name: " + name);
        System.out.println("Age: " + age);
        System.out.println("Height: " + height + " cm");
        
        // Step 4: Close the scanner
        sc.close();
    }
}
                

Scanner Class Methods

Method	Description	Return Type	Example
nextInt()	Reads an integer value	int	int age = sc.nextInt();
nextDouble()	Reads a double value	double	double price = sc.nextDouble();
nextFloat()	Reads a float value	float	float temp = sc.nextFloat();
next()	Reads a single word (till space)	String	String word = sc.next();
nextLine()	Reads a complete line	String	String line = sc.nextLine();
nextBoolean()	Reads a boolean value	boolean	boolean flag = sc.nextBoolean();
nextLong()	Reads a long value	long	long bigNum = sc.nextLong();
nextShort()	Reads a short value	short	short smallNum = sc.nextShort();

Practical Examples

Example 1: Student Information

import java.util.Scanner;

public class StudentInfo {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        
        System.out.println("=== Student Information ===");
        
        System.out.print("Enter student name: ");
        String name = sc.nextLine();
        
        System.out.print("Enter roll number: ");
        int rollNo = sc.nextInt();
        
        System.out.print("Enter marks in Math: ");
        int mathMarks = sc.nextInt();
        
        System.out.print("Enter marks in Science: ");
        int scienceMarks = sc.nextInt();
        
        System.out.print("Enter marks in English: ");
        int englishMarks = sc.nextInt();
        
        // Calculate total and average
        int total = mathMarks + scienceMarks + englishMarks;
        double average = total / 3.0;
        
        // Display results
        System.out.println("\n--- Student Report ---");
        System.out.println("Name: " + name);
        System.out.println("Roll No: " + rollNo);
        System.out.println("Total Marks: " + total + "/300");
        System.out.println("Average: " + average + "%");
        
        sc.close();
    }
}
                

Example 2: Temperature Converter

import java.util.Scanner;

public class TemperatureConverter {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        
        System.out.println("=== Temperature Converter ===");
        System.out.println("1. Celsius to Fahrenheit");
        System.out.println("2. Fahrenheit to Celsius");
        System.out.print("Enter your choice (1 or 2): ");
        
        int choice = sc.nextInt();
        
        if(choice == 1) {
            System.out.print("Enter temperature in Celsius: ");
            double celsius = sc.nextDouble();
            double fahrenheit = (celsius * 9/5) + 32;
            System.out.printf("%.2f°C = %.2f°F%n", celsius, fahrenheit);
        } else if(choice == 2) {
            System.out.print("Enter temperature in Fahrenheit: ");
            double fahrenheit = sc.nextDouble();
            double celsius = (fahrenheit - 32) * 5/9;
            System.out.printf("%.2f°F = %.2f°C%n", fahrenheit, celsius);
        } else {
            System.out.println("Invalid choice!");
        }
        
        sc.close();
    }
}
                

Common Issues and Solutions

Issue 1: nextLine() after nextInt()

When using nextLine() after nextInt(), the nextLine() might read the leftover newline character.

// Problem
System.out.print("Enter age: ");
int age = sc.nextInt();
System.out.print("Enter name: ");
String name = sc.nextLine(); // This might skip input

// Solution
System.out.print("Enter age: ");
int age = sc.nextInt();
sc.nextLine(); // Consume the leftover newline
System.out.print("Enter name: ");
String name = sc.nextLine();
                

Issue 2: Input Mismatch Exception

Occurs when the input doesn't match the expected data type.

import java.util.InputMismatchException;
import java.util.Scanner;

public class SafeInput {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        
        try {
            System.out.print("Enter an integer: ");
            int number = sc.nextInt();
            System.out.println("You entered: " + number);
        } catch(InputMismatchException e) {
            System.out.println("Invalid input! Please enter an integer.");
        }
        
        sc.close();
    }
}
                

Best Practices

Always close the Scanner to prevent resource leaks
Use appropriate data types for the input you expect
Handle exceptions when dealing with user input
Provide clear prompts to guide the user
Validate input before processing it
Use meaningful variable names for input values

Pro Tip: When reading multiple inputs, consider using separate Scanner objects for different input sources or be careful about mixing nextLine() with other nextXXX() methods.

Summary

Key Points Covered:

Output Methods: print(), println(), printf()
Input Methods: Scanner class and its various methods
Data Types: Different methods for different data types
Common Issues: Input mismatch and newline problems
Best Practices: Resource management and error handling

Remember: Input/Output operations are fundamental to programming. Mastering these concepts will help you create interactive and user-friendly applications.