我是Android应用程序开发的新手，现在我正在尝试制作一个简单的计算器应用程序。编译器没有检测到任何错误，并且成功下载到手机，但是在运行时它会收到一堆运行时错误。
public class MainActivity extends Activity {
Button one;
Button two;
Button three;
Button four;
Button five;
Button six;
Button seven;
Button eight;
Button nine;
Button add;
Button sub;
Button multiply;
Button divide;
Button clear;
Button equals;
String calculateNumber;
TextView textRead;
boolean ADD = false;
boolean SUB = false;
boolean MULTIPLY = false;
boolean DIVIDE = false;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//references all the objects within the XML file
one = (Button)findViewById(R.id.One);
two = (Button)findViewById(R.id.Two);
three = (Button)findViewById(R.id.Three);
four = (Button)findViewById(R.id.Four);
five = (Button)findViewById(R.id.Five);
six= (Button)findViewById(R.id.Six);
seven = (Button)findViewById(R.id.Seven);
eight= (Button)findViewById(R.id.Eight);
nine = (Button)findViewById(R.id.Nine);
add= (Button)findViewById(R.id.Add);
sub = (Button)findViewById(R.id.Sub);
multiply = (Button)findViewById(R.id.Multiply);
divide= (Button)findViewById(R.id.Divide);
equals = (Button)findViewById(R.id.Equal);
textRead = (TextView)findViewById(R.id.Numbers);
//Action listeners for each button to add it to the string
one.setOnClickListener(new Button.OnClickListener() {
public void onClick(View v) {
calculateNumber = calculateNumber + "1";
textRead.setText(calculateNumber);
}
});
two.setOnClickListener(new Button.OnClickListener() {
public void onClick(View v) {
calculateNumber = calculateNumber + "2";
textRead.setText(calculateNumber);
}
});
three.setOnClickListener(new Button.OnClickListener() {
public void onClick(View v) {
calculateNumber = calculateNumber + "3";
textRead.setText(calculateNumber);
}
});
four.setOnClickListener(new Button.OnClickListener() {
public void onClick(View v) {
calculateNumber = calculateNumber + "4";
textRead.setText(calculateNumber);
}
});
five.setOnClickListener(new Button.OnClickListener() {
public void onClick(View v) {
calculateNumber = calculateNumber + "5";
textRead.setText(calculateNumber);
}
});
six.setOnClickListener(new Button.OnClickListener() {
public void onClick(View v) {
calculateNumber = calculateNumber + "6";
textRead.setText(calculateNumber);
}
});
seven.setOnClickListener(new Button.OnClickListener() {
public void onClick(View v) {
calculateNumber = calculateNumber + "7";
textRead.setText(calculateNumber);
}
});
eight.setOnClickListener(new Button.OnClickListener() {
public void onClick(View v) {
calculateNumber = calculateNumber + "8";
textRead.setText(calculateNumber);
}
});
nine.setOnClickListener(new Button.OnClickListener() {
public void onClick(View v) {
calculateNumber = calculateNumber + "9";
textRead.setText(calculateNumber);
}
});
add.setOnClickListener(new Button.OnClickListener() {
public void onClick(View v) {
calculateNumber = calculateNumber + " + ";
ADD = true;
textRead.setText(calculateNumber);
}
});
sub.setOnClickListener(new Button.OnClickListener() {
public void onClick(View v) {
calculateNumber = calculateNumber + " - ";
SUB = true;
textRead.setText(calculateNumber);
}
});
multiply.setOnClickListener(new Button.OnClickListener() {
public void onClick(View v) {
calculateNumber = calculateNumber + " x ";
MULTIPLY = true;
textRead.setText(calculateNumber);
}
});
divide.setOnClickListener(new Button.OnClickListener() {
public void onClick(View v) {
calculateNumber = calculateNumber + " / ";
DIVIDE = true;
textRead.setText(calculateNumber);
}
});
clear.setOnClickListener(new Button.OnClickListener() {
public void onClick(View v) {
calculateNumber = "";
ADD = false;
SUB = false;
MULTIPLY = false;
DIVIDE = false;
textRead.setText(calculateNumber);
}
});
equals.setOnClickListener(new Button.OnClickListener() {
public void onClick(View v) {
//splits the one large string into two strings that can be parsable into Ints
String[] bothNumbers = calculateNumber.split("\\+");
double numberOne = 0;
double numberTwo = 0;
numberOne = Double.parseDouble(bothNumbers[0]);
numberTwo = Double.parseDouble(bothNumbers[1]);
if(ADD = true)
{
calculateNumber = "" + (numberOne+numberTwo);
ADD = false;
}
else if(SUB = true)
{
calculateNumber = "" + (numberOne - numberTwo);
SUB = false;
}
else if (MULTIPLY = true)
{
calculateNumber = "" + (numberOne*numberTwo);
MULTIPLY = false;
}
else if (DIVIDE = true)
{
calculateNumber = "" + (numberOne/numberTwo);
DIVIDE = false;
}
textRead.setText(calculateNumber);
}
});
}
}
这是我的一个Java文件，其中动作侦听器用于按钮。它应该没有任何问题，因为只有在按下按钮时才会调用它们。
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name="com.example.cakculator.MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
以下是eclipse给我的错误
06-20 10:48:16.678: E/AndroidRuntime(25231): FATAL EXCEPTION: main
06-20 10:48:16.678: E/AndroidRuntime(25231): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.cakculator/com.example.cakculator.MainActivity}: java.lang.NullPointerException
06-20 10:48:16.678: E/AndroidRuntime(25231): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1967)
06-20 10:48:16.678: E/AndroidRuntime(25231): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1992)
06-20 10:48:16.678: E/AndroidRuntime(25231): at android.app.ActivityThread.access$600(ActivityThread.java:127)
06-20 10:48:16.678: E/AndroidRuntime(25231): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1158)
06-20 10:48:16.678: E/AndroidRuntime(25231): at android.os.Handler.dispatchMessage(Handler.java:99)
06-20 10:48:16.678: E/AndroidRuntime(25231): at android.os.Looper.loop(Looper.java:137)
06-20 10:48:16.678: E/AndroidRuntime(25231): at android.app.ActivityThread.main(ActivityThread.java:4511)
06-20 10:48:16.678: E/AndroidRuntime(25231): at java.lang.reflect.Method.invokeNative(Native Method)
06-20 10:48:16.678: E/AndroidRuntime(25231): at java.lang.reflect.Method.invoke(Method.java:511)
06-20 10:48:16.678: E/AndroidRuntime(25231): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:976)
06-20 10:48:16.678: E/AndroidRuntime(25231): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:743)
06-20 10:48:16.678: E/AndroidRuntime(25231): at dalvik.system.NativeStart.main(Native Method)
06-20 10:48:16.678: E/AndroidRuntime(25231): Caused by: java.lang.NullPointerException
06-20 10:48:16.678: E/AndroidRuntime(25231): at com.example.cakculator.MainActivity.onCreate(MainActivity.java:152)
06-20 10:48:16.678: E/AndroidRuntime(25231): at android.app.Activity.performCreate(Activity.java:4486)
06-20 10:48:16.678: E/AndroidRuntime(25231): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1052)
06-20 10:48:16.678: E/AndroidRuntime(25231): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1931)
06-20 10:48:16.678: E/AndroidRuntime(25231): ... 11 more
如果你们能帮助我找到导致错误的事情，那就非常感激了！
答案 0 :(得分：4)
Button clear未设置 - ＆gt; NPE。