package org.eclipse.example.calc.internal.ui;
import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.border.TitledBorder;
import org.eclipse.example.calc.BinaryOperation;
import org.eclipse.example.calc.Operation;
import org.eclipse.example.calc.Operations;
import org.eclipse.example.calc.UnaryOperation;
import org.eclipse.example.calc.internal.operations.Equals;
import org.eclipse.example.calc.internal.operations.Minus;
import org.eclipse.example.calc.internal.operations.Plus;
import org.eclipse.example.calc.internal.operations.Square;
/*
* A simple calculator featuring a Swing UI.
*/
public class Calculator extends JFrame implements ActionListener {
private static final long serialVersionUID = 1L;
private String cmd;
private boolean clearDisplay;
private float value;
private JTextField display;
private JPanel buttonsPanel;
private JPanel numberButtonsPanel;
private JPanel cmdButtonsPanel;
private JButton numberButtons[];
private JButton cmdButtons[];
public static void main(String args[]) {
new Calculator().setVisible(true);
}
public Calculator() {
setupOperations();
setupGUI();
}
private void setupOperations() {
new Equals();
new Minus();
new Plus();
new Square();
}
private void setupGUI() {
setTitle("Simple Calculator");
Container c = getContentPane();
c.setLayout(new BorderLayout());
setupDisplay(c);
setupButtonsPanel(c);
setupNumberButtons();
setupCommandButtons();
pack();
}
private void setupDisplay(Container c) {
display = new JTextField("0");
display.setHorizontalAlignment(JTextField.TRAILING);
c.add(display, BorderLayout.NORTH);
// initially clear the display
clearDisplay = true;
}
private void setupButtonsPanel(Container c) {
buttonsPanel = new JPanel();
buttonsPanel.setLayout(new GridLayout(2, 1));
c.add(buttonsPanel);
}
private void setupNumberButtons() {
numberButtonsPanel = new JPanel();
numberButtonsPanel.setLayout(new GridLayout(3, 4));
buttonsPanel.add(numberButtonsPanel, BorderLayout.CENTER);
numberButtons = new JButton[11];
for (int i = 0; i < numberButtons.length - 1; i++) {
addNumberButton(i, Integer.valueOf(i).toString());
}
addNumberButton(10, ".");
}
private void addNumberButton(int i, String name) {
numberButtons[i] = new JButton();
numberButtons[i].setText(name);
numberButtons[i].addActionListener(this);
numberButtonsPanel.add(numberButtons[i]);
}
private void setupCommandButtons() {
// command buttons
cmdButtonsPanel = new JPanel();
cmdButtonsPanel.setLayout(new GridLayout(1, 0));
buttonsPanel.add(cmdButtonsPanel, BorderLayout.CENTER);
TitledBorder title = BorderFactory.createTitledBorder("Operations");
cmdButtonsPanel.setBorder(title);
cmdButtons = new JButton[Operations.INSTANCE.size()];
// make the buttons, set ActionListener and add to panel
for (int i = 0; i < cmdButtons.length; i++) {
addCommandButton(i);
}
}
private void addCommandButton(int i) {
cmdButtons[i] = new JButton();
cmdButtons[i].setText(Operations.INSTANCE.getOperationName(i));
cmdButtons[i].addActionListener(this);
cmdButtonsPanel.add(cmdButtons[i]);
}
public void actionPerformed(ActionEvent e) {
String str = e.getActionCommand();
if (isCommand(str)) {
calculate(str);
} else {
char digit = (str.toCharArray())[0];
if (Character.isDigit(digit) || digit == '.') {
if (clearDisplay) {
// save current value and clear the display
value = Float.parseFloat(display.getText());
display.setText("");
clearDisplay = false;
}
// add new digit to display
display.setText(display.getText() + digit);
}
}
}
private boolean isCommand(String name) {
return (Operations.INSTANCE.getOperation(name) != null);
}
private void calculate(String cmdName) {
float curValue;
float newValue = 0;
// get current value of display
curValue = Float.parseFloat(display.getText());
Operation currentOp = Operations.INSTANCE.getOperation(cmdName);
if ((currentOp instanceof BinaryOperation) && (cmd == null)) {
// if last clicked operation was binary and there is no saved
// operation, store it
cmd = cmdName;
clearDisplay = true;
} else {
// if saved command is binary perform it
Operation savedOp = Operations.INSTANCE.getOperation(cmd);
if (savedOp instanceof BinaryOperation) {
BinaryOperation bop = (BinaryOperation) savedOp;
newValue = bop.perform(value, curValue);
} // if current operation is unary perform it
else if (currentOp instanceof UnaryOperation) {
UnaryOperation uop = (UnaryOperation) currentOp;
newValue = uop.perform(curValue);
}
// display the result and prepare clear on next button
display.setText("" + newValue);
clearDisplay = true;
if (currentOp instanceof Equals) {
// do not save "=" command
cmd = null;
} else if (currentOp instanceof BinaryOperation) {
// save binary commands as they are executed on next operation
cmd = cmdName;
} else {
// clear saved command
cmd = null;
}
}
}
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short x = 999; // -32768 to 32767
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When ever you want to perform a set of operations based on a condition If-Else is used.
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Switch is an alternative to If-Else-If ladder and to select one among many blocks of code.
switch(<conditional-expression>) {
case value1:
// code
break; // optional
case value2:
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break; // optional
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default:
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}
For loop is used to iterate a set of statements based on a condition. Usually for loop is preferred when number of iterations is known in advance.
for(Initialization; Condition; Increment/decrement){
//code
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While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.
while(<condition>){
// code
}
Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.
do {
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Class is the blueprint of an object, which is also referred as user-defined data type with variables and functions. Object is a basic unit in OOP, and is an instance of the class.
class keyword is required to create a class.
class Mobile {
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public class Greeting {
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}
public static void main(String[] args) {
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Collection is a group of objects which can be represented as a single unit. Collections are introduced to bring a unified common interface to all the objects.
Collection Framework was introduced since JDK 1.2 which is used to represent and manage Collections and it contains:
This framework also defines map interfaces and several classes in addition to Collections.
| Collection | Description |
|---|---|
| Set | Set is a collection of elements which can not contain duplicate values. Set is implemented in HashSets, LinkedHashSets, TreeSet etc |
| List | List is a ordered collection of elements which can have duplicates. Lists are classified into ArrayList, LinkedList, Vectors |
| Queue | FIFO approach, while instantiating Queue interface you can either choose LinkedList or PriorityQueue. |
| Deque | Deque(Double Ended Queue) is used to add or remove elements from both the ends of the Queue(both head and tail) |
| Map | Map contains key-values pairs which don't have any duplicates. Map is implemented in HashMap, TreeMap etc. |