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import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.InputMismatchException;
import java.util.Random;
import java.util.Scanner;

public class Exceptions {

    // An exception is an event that occurs during the execution of a program

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public class Scoping {  // class scope begins

    // Because 'a' is declared just inside the *class curly braces* it is in 'class scope'
    // therefore its visible everywhere inside the class. This is the 'widest' scope in this file.
    private int a = 0;
    
    // Class variables have class scope!
    private static String classVariable = "I am a class variable!";

    public void methodOne() {  // methodOne scope begins

rshepherd

import java.util.Random;
 
public class Arrays {    
    public static void main(String[] args) {
        // Declaration style. 
        int arrayTwo[] = new int[3];
        int[] arrayOne = new int[3];   // This is better! []'s are part of the type!!

        // Indexing: We always refer to the first element of an array [0].
        // ex. subway example

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class DoublePointer {
  String s;
  public DoublePointer(String s){
    this.s = s;
  }
}

public class IdentitySwitch {
  public static void main(String[] args) {
    DoublePointer dp = new DoublePointer("unchanged");

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import java.util.ArrayList;
import java.util.List;

public class ForEach {

    public static void main(String[] args) {

        // Let's say we have a plain old array, like this one.
        char[] array = "This is a character array.".toCharArray();

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public class IdentitySwitch {
  public static void main(String[] args) {
    String s = "unchanged";
    System.out.println(s);
    foo(s);
    System.out.println(s);
  }
  
  public void foo(String s) {
    s = "changed"

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public class ListBasedQueue<T> implements Queue<T>
{
    private Node<T> first;      // beginning of queue
    private Node<T> last;       // For efficiency, maintain a reference to the least-recently added Node on the queue.

    public ListBasedQueue() {
        first = null;
        last = null;
    }

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import java.util.ArrayList;
import java.util.List;

public class ExpressionParser {

    public static void main(String[] arg) {
        // Assume the entered expression has only the expected characters otherwise they are ignored
        String input = "(400+8) * (6-5)/((311-2) *(2+2)) xxx";

        // Parse input

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import java.util.Scanner;

public class CommandObject {
    
    private static Scanner input = new Scanner(System.in);

    // a stubbed out example of how you can use OO to clean up 
    // how you take user input from the user.
    public static void main(String[] args) {
       Command c = getCommand();

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import java.util.ArrayList;

public class ParametricPolymorphism {

    public static void main(String[] args) {

        // Java Generics are an implementation of parametric polymorphism. They can be complicated subject.
        // We will only focus on their simple use case with collections (lists, sets, stacks, etc)

        // Old Java (1.4 and older):