<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"  xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"  android:layout_height="match_parent" >   <EditText    android:id="@+id/num1"    android:layout_width="80dp"    android:layout_height="wrap_content"     android:inputType="number" />    <TextView     android:id="@+id/type"    android:layout_width="40dp"    android:layout_height="50dp"    android:layout_toRightOf="@id/num1"    android:gravity="center" />   <EditText    android:id="@+id/num2"    android:layout_width="80dp"    android:layout_height="wrap_content"    android:layout_toRightOf="@id/num1"    android:layout_marginLeft="50dp"    android:inputType="number" />    <TextView    android:id="@+id/equal"    android:layout_width="80dp"    android:layout_height="50dp"    android:layout_toRightOf="@id/num2"    android:gravity="center" />    <Button     android:id="@+id/add"    android:layout_width="70dp"    android:layout_height="wrap_content"    android:layout_below="@id/num1"    android:text="@string/add" />   <Button     android:id="@+id/sub"    android:layout_width="70dp"    android:layout_height="wrap_content"    android:layout_toRightOf="@id/add"    android:layout_alignTop="@id/add"    android:text="@string/sub" />    <Button     android:id="@+id/mul"    android:layout_width="70dp"    android:layout_height="wrap_content"    android:layout_toRightOf="@id/sub"    android:layout_alignTop="@id/sub"    android:text="@string/mul" />    <Button     android:id="@+id/div"    android:layout_width="70dp"    android:layout_height="wrap_content"    android:layout_toRightOf="@id/mul"    android:layout_alignTop="@id/mul"    android:text="@string/div" /></RelativeLayout>

public class CalculatorBiz {  public float add(float num1,float num2){ return num1+num2; }  public float sub(float num1,float num2){ return num1-num2; }  public float mul(float num1,float num2){ return num1*num2; }  public float div(float num1,float num2){ return num1/num2; } }

public class MainActivity extends Activity {  //定義組件 private EditText inputnum1; private EditText inputnum2; private TextView type; private TextView equal; private Button add; private Button sub; private Button mul; private Button div; CalculatorBiz calculator=new CalculatorBiz();   @Override  public void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);    //查找組件    inputnum1=(EditText) findViewById(R.id.num1);    inputnum2=(EditText) findViewById(R.id.num2);    type=(TextView) findViewById(R.id.type);    equal=(TextView) findViewById(R.id.equal);    add=(Button) findViewById(R.id.add);    sub=(Button) findViewById(R.id.sub);    mul=(Button) findViewById(R.id.mul);    div=(Button) findViewById(R.id.div);        type.setTextColor(Color.WHITE);    equal.setTextColor(Color.WHITE);        add.setOnClickListener(new OnClickListener() {  @Override  public void onClick(View v) {  String num1=inputnum1.getText().toString();  String num2=inputnum2.getText().toString();  float a=Float.parseFloat(num1);  float b=Float.parseFloat(num2);  type.setText("+");  equal.setText("="+calculator.add(a, b));     }});    sub.setOnClickListener(new OnClickListener() {  @Override  public void onClick(View v) {  String num1=inputnum1.getText().toString();  String num2=inputnum2.getText().toString();  float a=Float.parseFloat(num1);  float b=Float.parseFloat(num2);  type.setText("-");  equal.setText("="+calculator.sub(a, b));     }});    mul.setOnClickListener(new OnClickListener() {  @Override  public void onClick(View v) {  String num1=inputnum1.getText().toString();  String num2=inputnum2.getText().toString();  float a=Float.parseFloat(num1);  float b=Float.parseFloat(num2);  type.setText("*");  equal.setText("="+calculator.mul(a, b));     }});    div.setOnClickListener(new OnClickListener() {  @Override  public void onClick(View v) {  String num1=inputnum1.getText().toString();  String num2=inputnum2.getText().toString();  float a=Float.parseFloat(num1);  float b=Float.parseFloat(num2);  type.setText("/");  equal.setText("="+calculator.div(a, b));     }});      }  @Override  public boolean onCreateOptionsMenu(Menu menu) {   super.onCreateOptionsMenu(menu);   menu.add(0, 1, 0, "關于");   menu.add(0, 2, 1, "退出");   menu.findItem(2);    return true;  }  public boolean onOptionsItemSelected(MenuItem item){   if(item.getItemId() == 1){         Toast.makeText(this, "詳細內容/n"+"作者：dyp/n"+"版本：version1", Toast.LENGTH_LONG).show();       }else if(item.getItemId() == 2){         Toast.makeText(this, "退出/n"+"你確定退出程序？", Toast.LENGTH_LONG).show();       }      return super.onOptionsItemSelected(item);  }   }