A calculator written in Google Web Toolkit

gwt-calc.java

/*
The MIT License

Copyright (c) 2011 Jim Schubert

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
*/

package com.schubert.test.client;

import com.google.gwt.core.client.EntryPoint;
import com.google.gwt.user.client.ui.Button;
import com.google.gwt.user.client.ui.ClickListener;
import com.google.gwt.user.client.ui.HasHorizontalAlignment;
import com.google.gwt.user.client.ui.Label;
import com.google.gwt.user.client.ui.FlexTable;
import com.google.gwt.user.client.ui.RootPanel;
import com.google.gwt.user.client.ui.TextBox;
import com.google.gwt.user.client.ui.VerticalPanel;
import com.google.gwt.user.client.ui.Widget;
import com.google.gwt.user.client.Window;

import java.util.ArrayList;

/**
 * Entry point classes define <code>onModuleLoad()</code>.
 */
public class myapp implements EntryPoint {

	private final String H_TEXT = "gwtCalc";
	private final String COMMON_WIDTH = "130px";
	private Label header = new Label();
	private TextBox displayArea = new TextBox();
	private FlexTable numTable = new FlexTable();
	private FlexTable clearsTable = new FlexTable();
	private VerticalPanel mainPanel = new VerticalPanel();
	private String[] syms = new String[] { "/", "x", "-", "+", "=" };
	private String[] clears = new String[] { "c", "ce", "%" };
	private String[] botRow = new String[] { ".", "0", "+-" };
	private ArrayList<String> eqParts = new ArrayList<String>();

	public void onModuleLoad() {
		// Create the buttons
		int row = 0;
		int column = 0;
		for (int i = 1; i < 16; i++) {
			Button btn = null;
			if (row == 0) {
				final String value = String.valueOf(i);

				btn = new Button(value);
				btn.addClickListener(new ClickListener() {
					public void onClick(Widget sender) {
						addToDisplay(value);
					}
				});
			} else if (row == 3) {
				if (i != 16) {
					final String value = botRow[column];

					btn = new Button(value);
					btn.addClickListener(new ClickListener() {
						public void onClick(Widget sender) {
							addToDisplay(value);
						}
					});
				}
			} else if (column == 3) {
				btn = null;
			} else {
				int adjusted = i - row;
				final String value = String.valueOf(adjusted);

				btn = new Button(value);
				btn.addClickListener(new ClickListener() {
					public void onClick(Widget sender) {
						addToDisplay(value);
					}
				});
			}

			numTable.setWidget(row, column, btn);
			column++;

			if ((i % 4) == 0) {
				// go to a new row, and go back to first column
				row++;
				column = 0;
			}
		}

		// Manually add the symbols (operators) and clear sets
		clearsTable.setWidget(0, 0, new Button(clears[0], new ClickListener() {
			public void onClick(Widget sender) {
				addToDisplay(clears[0]);
			}
		}));

		clearsTable.setWidget(0, 1, new Button(clears[1], new ClickListener() {
			public void onClick(Widget sender) {
				addToDisplay(clears[1]);
			}
		}));

		clearsTable.setWidget(0, 2, new Button(clears[2], new ClickListener() {
			public void onClick(Widget sender) {
				addToDisplay(clears[2]);
			}
		}));
		clearsTable.setWidget(0, 3, new Button(syms[0], new ClickListener() {
			public void onClick(Widget sender) {
				addToDisplay(syms[0]);
			}
		}));
		numTable.setWidget(0, 3, new Button(syms[1], new ClickListener() {
			public void onClick(Widget sender) {
				addToDisplay(syms[1]);
			}
		}));
		numTable.setWidget(1, 3, new Button(syms[2], new ClickListener() {
			public void onClick(Widget sender) {
				addToDisplay(syms[2]);
			}
		}));
		numTable.setWidget(2, 3, new Button(syms[3], new ClickListener() {
			public void onClick(Widget sender) {
				addToDisplay(syms[3]);
			}
		}));
		numTable.setWidget(3, 3, new Button(syms[4], new ClickListener() {
			public void onClick(Widget sender) {
				addToDisplay(syms[4]);
			}
		}));

		numTable.setWidth(COMMON_WIDTH);
		displayArea.setWidth(COMMON_WIDTH);
		header.setText(H_TEXT);
		header.setWidth(COMMON_WIDTH);

		// Construct the mainPanel in order (top to bottom)
		mainPanel.add(header);
		mainPanel.add(displayArea);
		mainPanel.add(clearsTable);
		mainPanel.add(numTable);

		// add styles
		mainPanel.addStyleName("gwt-VerticalPanel");
		mainPanel.addStyleName("calc");

		// add the mainPanel to the page
		RootPanel.get("calc").add(mainPanel);
	}

	private void addToDisplay(String addText) {
		String origText = new String();
		origText = displayArea.getText();

		if (ArrayContains(syms, addText)) {
			if (addText == "=") {
				// figure it out and clear the past
				eqParts.add(origText);
				FigureItOut();

				eqParts.clear();
				return;
			} else // anything else
			{
				// add to array
				if (displayArea.getText() != null)
					eqParts.add(origText);
				eqParts.add(addText);
				displayArea.setText("");
				return;
			}
		}

		if (addText == "+-") {
			if (origText.indexOf("-") > -1)
				displayArea.setText(origText.substring(1, origText.length()));
			else
				displayArea.setText("-" + origText);
		} else {
			if (addText == "%") {
				Double percent = null;
				percent = Double.parseDouble(origText) / 100;

				displayArea.setText(percent.toString());
				return;
			}
			if (addText == "c") {
				displayArea.setText("");
				return;
			}
			if (addText == "ce") {
				displayArea.setText("");
				eqParts.clear();
				return;
			}
			if (addText == ".") {
				if (origText.indexOf(".") > -1)
					return;
				else
					displayArea.setText(origText + addText);
			} else {
				displayArea.setText(origText + addText);
			}
		}
	}

	private void FigureItOut() {
		// set displayArea text to the answer
		Double answer = null;
		Double firstNum = null;
		Double nextNum = null;
		String operator = null;

		for (int i = 0; i < eqParts.size(); i++) {
			String currVal = eqParts.get(i);
			boolean isOperator = false;
			isOperator = ArrayContains(syms, currVal);

			// add a number
			if (firstNum == null) {
				firstNum = Double.parseDouble(currVal);
				// Window.alert(firstNum.toString());
				continue;
			} else if (isOperator == true && i == 0) {
				Window.alert("Try again!");
				eqParts.clear();
				return;
			} else if (isOperator == true) {
				if (i == eqParts.size()) {
					Window.alert("You may not end with an operator");
					eqParts.clear();
					displayArea.setText("");
					return;
				}
				operator = currVal;
				// Window.alert(operator);
				continue;
			} else if (nextNum == null) {
				nextNum = Double.parseDouble(currVal);
				// Window.alert(nextNum.toString());

				if (operator == "+") {
					answer = firstNum + nextNum;
				} else if (operator == "-") {
					answer = firstNum - nextNum;
				} else if (operator == "x") {
					answer = firstNum * nextNum;
				} else if (operator == "/") {
					answer = firstNum / nextNum;
				} else if (operator == "=") {
				} // do nothing?
				else {
				} // do someting?

				displayArea.setText(answer.toString());

				// Window.alert("The answer is " + answer);
				firstNum = answer;
				nextNum = null;
				operator = null;
			} else {
				Window.alert("Something unexpected happened. Try again.");
			}
		}
	}

	private boolean ArrayContains(String[] array, String check) {
		boolean found = false;
		for (int i = 0; i < array.length; i++) {
			if (check == array[i])
				return true;
		}

		return found;
	}
}

I wrote this ~3 years ago just to take a look at the Google Web Toolkit API. I haven't modified it since.