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content/ta/fall2017/cpsc220/nov13.md

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+# Lecture for November 13
+
+## File IO (Cont.)
+
+Last class we talked about reading from files, we can also write to files.
+
+### Import necessary libraries
+
+First you must import all of the necessary libraries
+
+```java
+// To read 
+import java.util.Scanner; 
+import java.io.FileOutputStream;
+// To Write
+import java.io.FileReader;
+import java.io.PrintWriter;
+// For Exception Handling
+import java.io.IOException;
+```
+
+Then in your main, declare a `FileOutputStream` and `PrintWriter`
+
+```java
+FileOutputStream file;
+PrintWriter print;
+```
+
+### Try-Catch-Finally
+
+Create a try block to open a file for writing
+
+```java
+try {
+      // If the file doesn't exist, it'll create it
+      file = new FileOutputStream("output.txt"); 
+      print = new PrintWriter(file);
+} catch (IOException except) {
+      // Prints out the error message
+      System.out.println("File error " + except.getMessage()); 
+} 
+```
+
+Adding a finally block allows the program to clean up before it closes
+
+```java
+    try {
+      file = new FileOutputStream("output.txt"); 
+      print = new PrintWriter(file);
+    } catch (IOException except) {
+      System.out.println("File error " + except.getMessage()); 
+    } finally { // It starts here!
+      delete file;
+      delete print;
+      file.close();
+      return;
+    }
+```
+
+### Write to the file :)
+
+Then you can write the to file!
+
+```java
+// Do you notice the following methods?
+  print.println("Your number is");
+  print.print("My name is..\n");
+  print.printf("%s %d", "Hello ", 5);
+  print.flush(); //Clears the output stream
+  file.close(); //Closes the file
+
+```
+
+Extra Note: Disk fragmentation is a way of cleaning up memory that isn't being used by any of the code on your computer. 
+
+## Swing Graphics
+
+### Importing Necessary Libraries
+
+
+
+You need to import all the necessary libraries first
+
+```java
+import javax.swing.*;
+import java.awt.FlowLayout;
+import java.awt.event.ActionListener;
+```
+
+### Changing the class header
+
+Your class file needs to extend `JFrame` that way it can use a bunch of the already existent code written for Swing applications
+
+```java
+public class firstGUi extends JFrame {
+  //....
+```
+
+### Swing Components
+
+Java Swing makes use of what is called Swing Components. These are basic building blocks of GUI items you can add to the screen. For example, a checkbox, a radio button, text field. These are all swing components.
+
+I wrote a blog post back in the summer which is an overview of them. You can check it out here: https://brandonrozek.com/2017/06/java-swing-components/
+
+Inside your `firstGUI` class, declare some Swing components you would like to use in the program
+
+```java
+public class firstGUI extends JFrame {
+  JButton button1;
+  JTextArea area;
+  JTextField text;
+  // ....
+
+```
+
+### Constructor
+
+You need to create a constructor for this class that way you can initiate all of the swing component values.
+
+```java
+// ...
+JButton button1;
+JTextArea area;
+JTextField text;
+
+// Begin Constructor
+firstGUI() {
+  // Define the components
+  JLabel name = new JLabel("Enter in your name:");
+  text = new JTextField("Jennifer", 20); // 20 characters long, default value: Jennifer
+  area = new JTextArea(10, 10); //Width and Height is 10 characters big
+  JScrollPane sp = new JScrollPane(area); //Adds a scroll bar for the text area
+  button1 = new JButton("Press Me");
+  
+  // Set the Layout
+  // FlowLayout organizes each of the components top to bottom, left to right
+  setLayout(new FlowLayout()); 
+  
+  // Add the components to the screen
+  add(name);
+  add(text);
+  add(sp); // never add the textarea when surrounded by a ScrollPane
+  add(button1);
+}
+```
+
+### New Main Method
+
+Finally, you need to create the Main method which will initiate it all
+
+```java
+public static void main(String[] args) {
+  firstGUI myFrame = new firstGUI();
+  
+  // End the program when the 'x' button (not keyboard) is pressed
+  myFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
+  
+  myFrame.setTitle("My title"); // Titles the window
+  myFrame.pack(); // Packs it all into the frame
+  myFrame.setVisible(true); // Makes the frame appear on the screen
+}
+```
+
+### Making it interactive
+
+You need to change your class header to the following
+
+```java
+public class firstGUI extends JFrame implements ActionListener {
+  // ...
+```
+
+Then in your class, add the following method
+
+```java
+@Override public void actionPerformed(ActionEvent event) {
+  // Do stuff as a result of an event here
+  area.append("You Pressed the Button");
+}
+```
+
+To make it actually activate as a result of an event. You need to attach it to a swing component.
+
+For example, I want the code in `actionPerformed` to activate in result of a button press.
+
+Add the following line to your code in the constructor.
+
+```java
+//...
+button1 = new JButton("Press Me");
+button1.addActionListener(this); // New Code
+//....
+```
+
+
+
+### Identifying Button Pressed
+
+How do you know which button was pressed in the `actionPerformed` method?
+
+You can use `event.getSource()` to find out.
+
+Example:
+
+```java
+@Override public void actionPerformed(ActionEvent event) {
+  if (event.getSource() == button1) { // Replace button1 with appropriate variable name
+    // Do things as a result of a specific button being pressed
+  }
+}
+```
+
+### Summary
+
+To use Swing, do the following steps
+
+1. Import Libraries
+2. Declare J___ variables
+3. New the J___ variables
+4. Add the J___ variables to the frame
+5. Add the `ActionListener` to the components you wish to monitor