User Input with Scanner

The Scanner class from java.util package enables reading user input. Here's the basic syntax:

InputReader reader = new InputReader(System.in);

Use next() and nextLine() methods to read strings, with hasNext() and hasNextLine() to check for available input.

next() Method

import java.util.Scanner;

public class InputExample {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.print("Enter text: ");
        
        String text = input.next();
        System.out.println("You entered: " + text);
        
        input.close();
    }
}

Output when entering "hello world":

Enter text: hello world
You entered: hello

Key characteristics of next():

• Requires valid input characters before completion
• Ignores leading whitespace
• Treats trailing whitespace as delimiters
• Cannot read strings containing spaces

Reading Different Data Types

import java.util.Scanner;

public class MultiTypeInput {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        
        System.out.print("Enter integer: ");
        if(input.hasNextInt()) {
            int number = input.nextInt();
            System.out.println("Integer: " + number);
        }
        
        System.out.print("Enter decimal: ");
        if(input.hasNextFloat()) {
            float decimal = input.nextFloat();
            System.out.println("Decimal: " + decimal);
        }
        
        input.close();
    }
}

nextLine() Method

import java.util.Scanner;

public class LineInput {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.print("Enter text: ");
        
        String text = input.nextLine();
        System.out.println("Full line: " + text);
        
        input.close();
    }
}

Output when entering " hello world":

Enter text:     hello world
Full line:     hello world

Key characteristics of nextLine():

• Reads until Enter key is pressed
• Returns all character including spaces
• Preserves leading and trailing whitespace

Sequential Execution

Java executes code sequentially by default, processing statements in the order they appear unles directed otherwise by control structures.

Conditional Statements

Single if Statement

if(condition) {
    // Executes when condition is true
}

if-else Statement

if(condition) {
    // True branch
} else {
    // False branch
}

Multiple Conditions

if(condition1) {
    // First true case
} else if(condition2) {
    // Second true case
} else if(condition3) {
    // Third true case
} else {
    // All false case
}

Nested if Statements

if(outerCondition) {
    if(innerCondition) {
        // Both conditions true
    }
}

Switch Statement

switch(variable) {
    case value1:
        // Code for value1
        break;
    case value2:
        // Code for value2
        break;
    default:
        // Default case
}

Switch supports byte, short, int, char, and String types. Each case must be a constant value.

Loop Structures

While Loop

while(condition) {
    // Loop body
}

Do-While Loop

do {
    // Loop body
} while(condition);

For Loop

for(initialization; condition; update) {
    // Loop body
}

Enhanced For Loop

for(dataType element : collection) {
    // Process element
}

public class ArrayIteration {
    public static void main(String[] args) {
        int[] values = {10, 20, 30, 40};
        
        for(int value : values) {
            System.out.println(value);
        }
    }
}

Loop Control: Break and Continue

Break Statement

public class BreakExample {
    public static void main(String[] args) {
        int counter = 0;
        while(counter < 100) {
            counter++;
            System.out.println(counter);
            if(counter == 30) {
                break;
            }
        }
    }
}

Continue Statement

public class ContinueExample {
    public static void main(String[] args) {
        int number = 0;
        while(number < 10) {
            number++;
            if(number % 2 == 0) {
                continue;
            }
            System.out.println(number);
        }
    }
}

Labeled Statements

public class PrimeNumbers {
    public static void main(String[] args) {
        outer: for(int num = 101; num < 150; num++) {
            for(int divisor = 2; divisor < num/2; divisor++) {
                if(num % divisor == 0) {
                    continue outer;
                }
            }
            System.out.println(num);
        }
    }
}