Android App - Basic calculator

Default.java

package com.woplandia.calc;

import java.util.HashSet;
import java.util.Set;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class Default extends Activity {

	private TextView result;

	private String operand;

	private String operator;

	private Set<String> numbers;

	private Set<String> operators;

	/** Called when the activity is first created. */
	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);

		result = (TextView) findViewById(R.id.result);
	}

	/**
	 * Initialization of set of number values.
	 */
	private void initNumbers() {
		numbers = new HashSet<String>();
		for (int i = 0; i < 10; i++) {
			numbers.add(Integer.toString(i));
		}
	}

	/**
	 * Initialization of set of operators.
	 */
	private void initOperators() {
		operators = new HashSet<String>();
		String[] ops = { "+", "-", "*", "/" };
		for (String operator : ops) {
			operators.add(operator);
		}
	}

	/**
	 * Button click event handler.
	 * 
	 * @param view clicked button
	 * @return void
	 */
	public void handleClick(View view) {
		Button clicked = (Button) view;
		String label = clicked.getText().toString();
		String display = result.getText().toString();
		
		if (isClear(label)) {
			result.setText(R.string.result_default);
		} else if (isNumerical(label)) {
			if (isDefaultResult(display) || isOperator(display)) {
				result.setText(label);
			} else {
				result.setText(display + label);
			}
		} else if (isOperator(label)) {
			operator = label;
			operand = display;
			result.setText(label);
		} else if (label.equals("=")) {
			double a, b, c;
			
			if (operator == null || operand == null) {
				return;
			}
			
			try {
				a = Double.parseDouble(operand);
				b = Double.parseDouble(display);
			}
			catch (Exception e) {
				System.out.println(e.getMessage());
				return;
			}
			
			if (operator.equals("+")) {
				c = a + b;
			} else if (operator.equals("-")) {
				c = a - b;
			} else if (operator.equals("*")) {
				c = a * b;
			} else  {
				c = a / b;
			}
			
			operand = Double.toString(c);
			result.setText(operand);
		}
	}

	/**
	 * Test if value is the same as clear button's.
	 * 
	 * @param value button value
	 * @return true if button is clear button
	 */
	private boolean isClear(String value) {
		return value.equals(getString(R.string.buttonClear));
	}

	/**
	 * Test if value is operator.
	 * 
	 * @param value
	 *            button value
	 * @return true if value is operator
	 */
	private boolean isOperator(String value) {
		if (operators == null) {
			initOperators();
		}
		return operators.contains(value);
	}

	/**
	 * Test if result was modified.
	 * 
	 * @param value result value
	 * @return true if result is default
	 */
	private boolean isDefaultResult(String value) {
		return value.equals(getString(R.string.result_default));
	}

	/**
	 * Test if value is numerical.
	 * 
	 * @param value button's value
	 * @return true if value is numerical
	 */
	private boolean isNumerical(String value) {
		if (numbers == null) {
			initNumbers();
		}
		return numbers.contains(value);
	}

}

main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
    <TableLayout
    	android:id="@+id/tableLayout1"
    	android:layout_height="fill_parent"
    	android:layout_width="fill_parent">
		<TextView
			android:id="@+id/result"
			android:layout_height="25pt"
			android:textSize="14pt"
			android:padding="4pt"
			android:gravity="right"
			android:text="@string/result_default"
		/>
		<View
        	android:layout_height="2dip"
        	android:background="#FF909090" />
        
        <TableRow
        	android:layout_height="wrap_content"
        	android:layout_width="match_parent"
        	android:layout_marginTop="5pt"
        	android:id="@+id/tableRow2"
        	android:paddingLeft="4pt"
        	android:paddingRight="4pt">
            <Button
            	android:text="@string/buttonSeven"
            	android:textSize="14pt"
            	android:id="@+id/button7"
            	android:layout_width="25pt"
            	android:layout_height="25pt"
            	android:layout_weight="1"
            	android:onClick="handleClick" />
            <Button
            	android:text="@string/buttonEight"
            	android:textSize="14pt"
            	android:id="@+id/button8"
            	android:layout_height="25pt"
            	android:layout_width="25pt"
            	android:layout_weight="1"
            	android:onClick="handleClick" />
            <Button
            	android:text="@string/buttonNine"
            	android:textSize="14pt"
            	android:id="@+id/button9"
            	android:layout_width="25pt"
            	android:layout_height="25pt"
            	android:layout_weight="1"
            	android:onClick="handleClick" />
            <Button
            	android:text="@string/buttonDivide"
            	android:textSize="14pt"
            	android:id="@+id/buttonDivide"
            	android:layout_width="25pt"
            	android:layout_height="25pt"
            	android:layout_weight="1"
            	android:onClick="handleClick" />
        </TableRow>
        
        <TableRow
        	android:layout_height="wrap_content"
        	android:layout_width="match_parent"
        	android:layout_marginTop="1pt"
        	android:id="@+id/tableRow2"
        	android:paddingLeft="4pt"
        	android:paddingRight="4pt">
            <Button
            	android:text="@string/buttonFour"
            	android:textSize="14pt"
            	android:id="@+id/button4"
            	android:layout_width="25pt"
            	android:layout_height="25pt"
            	android:layout_weight="1"
            	android:onClick="handleClick" />
            <Button
            	android:text="@string/buttonFive"
            	android:textSize="14pt"
            	android:id="@+id/button5"
            	android:layout_height="25pt"
            	android:layout_width="25pt"
            	android:layout_weight="1"
            	android:onClick="handleClick" />
            <Button
            	android:text="@string/buttonSix"
            	android:textSize="14pt"
            	android:id="@+id/button6"
            	android:layout_width="25pt"
            	android:layout_height="25pt"
            	android:layout_weight="1"
            	android:onClick="handleClick" />
            <Button
            	android:text="@string/buttonMutiply"
            	android:textSize="14pt"
            	android:id="@+id/buttonMultiply"
            	android:layout_width="25pt"
            	android:layout_height="25pt"
            	android:layout_weight="1" 
            	android:onClick="handleClick" />
        </TableRow>
        
        <TableRow
        	android:layout_height="wrap_content"
        	android:layout_width="match_parent"
        	android:layout_marginTop="1pt"
        	android:id="@+id/tableRow2"
        	android:paddingLeft="4pt"
        	android:paddingRight="4pt">
            <Button
            	android:text="@string/buttonOne"
            	android:textSize="14pt"
            	android:id="@+id/button1"
            	android:layout_width="25pt"
            	android:layout_height="25pt"
            	android:layout_weight="1"
            	android:onClick="handleClick" />
            <Button
            	android:text="@string/buttonTwo"
            	android:textSize="14pt"
            	android:id="@+id/button2"
            	android:layout_height="25pt"
            	android:layout_width="25pt"
            	android:layout_weight="1"
            	android:onClick="handleClick" />
            <Button
            	android:text="@string/buttonThree"
            	android:textSize="14pt"
            	android:id="@+id/button3"
            	android:layout_width="25pt"
            	android:layout_height="25pt"
            	android:layout_weight="1"
            	android:onClick="handleClick" />
            <Button
            	android:text="@string/buttonMinus"
            	android:textSize="14pt"
            	android:id="@+id/buttonMinus"
            	android:layout_width="25pt"
            	android:layout_height="25pt"
            	android:layout_weight="1"
            	android:onClick="handleClick" />
        </TableRow>
        
         <TableRow
        	android:layout_height="wrap_content"
        	android:layout_width="match_parent"
        	android:layout_marginTop="1pt"
        	android:id="@+id/tableRow2"
        	android:paddingLeft="4pt"
        	android:paddingRight="4pt">
            <Button
            	android:text="@string/buttonClear"
            	android:textSize="14pt"
            	android:id="@+id/buttonClear"
            	android:layout_width="25pt"
            	android:layout_height="25pt"
            	android:layout_weight="1"
            	android:onClick="handleClick" />
            <Button
            	android:text="@string/buttonZero"
            	android:textSize="14pt"
            	android:id="@+id/button0"
            	android:layout_height="25pt"
            	android:layout_width="25pt"
            	android:layout_weight="1"
            	android:onClick="handleClick" />
            <Button
            	android:text="@string/buttonResult"
            	android:textSize="14pt"
            	android:id="@+id/buttonResult"
            	android:layout_width="25pt"
            	android:layout_height="25pt"
            	android:layout_weight="1"
            	android:onClick="handleClick" />
            <Button
            	android:text="@string/buttonPlus"
            	android:textSize="14pt"
            	android:id="@+id/buttonPlus"
            	android:layout_width="25pt"
            	android:layout_height="25pt"
            	android:layout_weight="1"
            	android:onClick="handleClick" />
        </TableRow>
    </TableLayout>
</LinearLayout>

strings.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <string name="hello">Hello World, Default!</string>
    <string name="app_name">Dummy Calc</string>
    
    <string name="result_default">0</string>
    
    <string name="buttonPlus">+</string>
    <string name="buttonMinus">-</string>
    <string name="buttonMutiply">*</string>
    <string name="buttonDivide">/</string>
    <string name="buttonClear">C</string>
    <string name="buttonResult">=</string>
    
    <string name="buttonZero">0</string>
    
    <string name="buttonOne">1</string>
    <string name="buttonTwo">2</string>
    <string name="buttonThree">3</string>
    
    
    <string name="buttonFour">4</string>
    <string name="buttonFive">5</string>
    <string name="buttonSix">6</string>
    
    <string name="buttonSeven">7</string>
    <string name="buttonEight">8</string>
    <string name="buttonNine">9</string>
</resources>