Java CheatSheet

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SCANNER
Scanner sc = new Scanner(System.in);//new File("myNumbers") for parsing files
int i = sc.nextInt();
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FILE READ
//do try with finally where close the streams
BufferedReader in = new BufferedReader(new FileReader("employee.txt"));//in.readLine()
StringTokenizer t = new StringTokenizer(s,"token");//t.nextToken()
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FILE CLASS
File file = new File("test");
.exists(), .isFile(), .isDirectory(), .getName(), .getPath(), .length()
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Multitasking : more than one process at a time; CPU time distributed among processes
Preemptive Multitasking: OS interrupts processes without waiting them to release CPU
Co-Operative Multitasking: processes willing to yield control
Threads get a portion of the CPU
Threads not run in order thay are created
Thread 4 states: new, runnable, blocked, dead *blocked thread reenters runnable using the same route that blocked it*
                thread dies when void run() finished normally or dies randomly caused by execption
Sunchronization in java : Exclusion sync *mutual exclusion*, Condition sync

public myRunnable implements Runnable{

    myRunnable() {
        (new Thread(this)).start();
    }

    @Override
    public void run() {
        //do stuff
    }
}

while (!Thread.currentThread().isInterrupted() && workToDo()) {
    //do work
    //if interrupted method is called on a blocked thread *waiting for stuff* the thread will be terminated by an InterrptedException
}

synchronized (expression) {
    //doWork
    //sync guarantees expression will not be modified by any other thread. called client-side sync
}

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NETWORKING
Request : sync *client waits for response* async*client proceeds computatuin before having response*
Server: *waits, listens* on IP+PORT; called host machine *PORT 2 byte number 0-1023 well known ports, 1024-49151 your ports, 49152-65535 not registered*
Socket s = new Socket(host, port);
public class myServer {
    private static final int PORT;

    myServer(int port) {
        this.PORT = port;
    }

    public void startServer throws IOException {
        ServerSocket s = new ServerSocket(PORT);
        try {
            while (true) {
                Socket socket = s.accept();
                try {
                    new myServerThreader(socket);
                } catch (IOException e) {
                    socket.close();
                }
            }
        }
        finally {
            s.close();
        }
    }
}

public class myServerThreader implements Runnable {
    private Socket socket;
    private BufferedReader in;
    private PrintWriter out;

    myServerThreader(Socket socket) {
        this.socket = socket;
        this.in = new BufferedReader (new InputStreamReader (this.socket.getInputStream()));
        this.in = new PrintWriter (new OutputStreamWriter (this.socket.getOutputStream()), true);
        (new Thread(this)).start();
    }
}

URL url = new URL(string);
InputStream inStream = url.openStream();
BufferedReader in = new BufferedReader(mew InputStreamReader(inStream));

URL connection class to get more info about web resource
URLConnection conn = url.openConnection();
conn.connect();//to connect
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GUI
event source and handler binding is done at runtime, registration is done by passing refference, done when program starts
JLabel, JTextField, JButton, JCheckBox, JComboBox, JList, JPanel
{}
JPanel :
    FlowLayout default; puts them in line and where is no space makes new row; auto reflow
        panel.setLayout(new FlowLayout(FlowLayout.LEFT)); //default CENTER
    BorderLayout default for JFrame, can place components CENTER NORTH SOUTH EAST WEST
        panel.setLayout(new BorderLayout());
        panel.add(yellowButton, BorderLayout.SOUTH);
    GridLayout puts them like a spreadsheet *row, cols* cells have same size
        panel.setLayout(new GridLayout(5,4)); //5 rows 4 cols

JTextField :
        new JTextField("Default text", 20);
        void setText(string);
        String getText();
        void setEditable(boolean b);

JLabel :
    new JLabel("Default text", JLabel.RIGHT);

JPasswordField :
    new JPasswordField("Default Text", int columns);
    char[] getPassword();
    void setEchoChar(char echo);

JFormattedTextField :
    DateFormat.getDateInstance
              .getTimeInstance
              .getDateTimeInstance
    new JFormattedTextField(NumberFormat.getIntegerInstance());
    int x = ((Number) txtField.getValue()).intValue();

JTextArea :
    new JTextArea(8,40)
    void setLineWrap(boolean b)
    JScrollPane jScroll = new JScrollPane(textArea);

JCheckBox :
    new JCheckBox("Text");
    void setSelected(boolean b);
    boolean isSelected();
    ActionListener listener = new ActionListener(actionPerformed)
    JCheckBox.addActionListener (listener);
    public void actionPerformed )ActionEvent e) {
        //doShit based on event
    }

JRadioButton :
    ButtonGroup gr;
    new JRadioButton("Small", false);
    gr.add(RadioButton);

JComboBox<String> :
    .setEditable(true);
    .addItem("da");
    .getSelected();
    .removeItem("");

//make menu bar
JMenuBar menuBar = new JMenuBar();
frame.setMenuBar(menuBar);

//add menu to menubar
JMenu editMenu = new JMenu(“Edit“);
menuBar.add(editMenu);

//add item to menu
JMenuItem pasteItem = new JMenuItem("Paste");
editMenu.add(pasteItem);
editMenu.addSeparator();
pasteItem.addActionListener(listener);



//add action to menu
JMenuItem menuItemClose = new JMenuItem("Close");
menuItemClose.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent e) {
        System.exit(0);
    }
});
menu.add(menuItemClose);


//add menu item with picture
JMenuItem cutItem = new JMenuItem("Cut", new ImageIcon("cut.gif"));


JCheckBoxMenuItem readonlyItem = new JCheckBoxMenuItem("Read-only");
optionsMenu.add(readonlyItem);

//popup menu
JPopupMenu popup = new JPopupMenu();
    JMenuItem item = new JMenuItem("Cut");
    item.addActionListener(listener);
popup.add(item);
component.setComponentPopupMenu(popup);

//toolbar
JToolBar bar = new JToolBar();
    bar.add(blueButton);
add(bar, BorderLayout.NORTH);
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Dialog
int selection = JOptionPane.showConfirmDialog(parent, "Message", "Title",
                JOptionPane.OK_CANCEL_OPTION, JOptionPane.WARNING_MESSAGE);
if (selection == JOptionPane.OK_OPTION) {
    //doShit
}

public AboutDialog extends JDialog {
    public AboutDialog(JFrame owner) {
        super (owner, "Title", true);
        add(new JLabel("Text"), BorderLayout.CENTER);
        JButton ok = new JButton("OK");
        ok.addActionListener( new
            ActionListener() {
                public void actionperformed(ActionEvent event) {
                    //doShit
                    setVisible(false);
                }
            });
        add(ok, BorderLayout.SOUTH);
        setSize(100,100);
    }
}
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OpenDialog
JFileChooser chooser = new JFileChooser();
chooser.setFileFilter(new FileFilter() {
       @Override
       public String getDescription() {return "File desc";}
       @Override
       public boolean accept(File f) {
            if (f.isDirectory()) {
                return true;
            } else {
                return f.getName().toLowerCase().endsWith(".png");
            }
        }
    });
chooser.setFileSelectionMode(JFileChooser.FILES_ONLY);
chooser.setCurrentDirectory(new File("location"));
int res = chooser.showOpenDialog(JFileChooserEx.this);
if (res == JFileChooser.APPROVE_OPTION) {
    File file = chooser.getSelectedFile();
} else {
    JOptionPane.showMessageDialog(this, "Dialog cancelled by the user");
}
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SaveDialog
JFileChooser fileChooser = new JFileChooser();
fileChooser.setDialogTitle("Specify a file to save");

int userSelection = fileChooser.showSaveDialog(parentFrame);

if (userSelection == JFileChooser.APPROVE_OPTION) {
    File fileToSave = fileChooser.getSelectedFile();
    System.out.println("Save as file: " + fileToSave.getAbsolutePath());
}
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public class Example extends JFrame {

    public Example() {
        initUI();
    }

    public final void initUI() {

        JMenuBar menubar = new JMenuBar();
        ImageIcon icon = new ImageIcon(getClass().getResource("exit.png"));

        JMenu file = new JMenu("File");
        file.setMnemonic(KeyEvent.VK_F);

        JMenuItem eMenuItem = new JMenuItem("Exit", icon);
        eMenuItem.setMnemonic(KeyEvent.VK_E);
        eMenuItem.setToolTipText("Exit application");
        eMenuItem.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent event) {
                System.exit(0);
            }
        });

        file.add(eMenuItem);

        menubar.add(file);
        addSeparator();
        setJMenuBar(menubar);

        setTitle("Simple menu");
        setSize(300, 200);
        setLocationRelativeTo(null);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
    }

    public static void main(String[] args) {

        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                Example ex = new Example();
                ex.setVisible(true);
            }
        });
    }
}
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IMPORTS
import java.io.*;
import java.net.*;
import java.util.*;
import java.awt.*;
import javax.swing.*;
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