谁能告诉我这些错误的含义，实际上我是android编码的新手，无法弄清楚这些错误，请帮忙。
06-11 11:56:08.118: W/dalvikvm(593): threadid=1: thread exiting with uncaught exception (group=0x409c01f8)
06-11 11:56:08.128: E/AndroidRuntime(593): FATAL EXCEPTION: main
06-11 11:56:08.128: E/AndroidRuntime(593): java.lang.RuntimeException: Unable to start activity ComponentInfo{gaurav.android/gaurav.android.CalcActivity}: java.lang.NullPointerException
06-11 11:56:08.128: E/AndroidRuntime(593): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
06-11 11:56:08.128: E/AndroidRuntime(593): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
06-11 11:56:08.128: E/AndroidRuntime(593): at android.app.ActivityThread.access$600(ActivityThread.java:123)
06-11 11:56:08.128: E/AndroidRuntime(593): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
06-11 11:56:08.128: E/AndroidRuntime(593): at android.os.Handler.dispatchMessage(Handler.java:99)
06-11 11:56:08.128: E/AndroidRuntime(593): at android.os.Looper.loop(Looper.java:137)
06-11 11:56:08.128: E/AndroidRuntime(593): at android.app.ActivityThread.main(ActivityThread.java:4424)
06-11 11:56:08.128: E/AndroidRuntime(593): at java.lang.reflect.Method.invokeNative(Native Method)
06-11 11:56:08.128: E/AndroidRuntime(593): at java.lang.reflect.Method.invoke(Method.java:511)
06-11 11:56:08.128: E/AndroidRuntime(593): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
06-11 11:56:08.128: E/AndroidRuntime(593): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
06-11 11:56:08.128: E/AndroidRuntime(593): at dalvik.system.NativeStart.main(Native Method)
06-11 11:56:08.128: E/AndroidRuntime(593): Caused by: java.lang.NullPointerException
06-11 11:56:08.128: E/AndroidRuntime(593): at gaurav.android.CalcActivity.reset(CalcActivity.java:341)
06-11 11:56:08.128: E/AndroidRuntime(593): at gaurav.android.CalcActivity.onCreate(CalcActivity.java:58)
06-11 11:56:08.128: E/AndroidRuntime(593): at android.app.Activity.performCreate(Activity.java:4465)
06-11 11:56:08.128: E/AndroidRuntime(593): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
06-11 11:56:08.128: E/AndroidRuntime(593): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)
这是我的代码，它实际上是一个简单的计算器。
包gaurav.android；
import android.app.Activity;
import android.os.Bundle;
import android.view.KeyEvent;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnKeyListener;
import android.widget.Button;
import android.widget.EditText;
public class CalcActivity extends Activity {
EditText t=null;
private final int MENUITEM_CLOSE = 300;
private boolean hasChanged;
private boolean readyToClear;
public Button b1=null;
public Button b2=null;
public Button b3=null;
public Button b4=null;
public Button b5=null;
public Button b6=null;
public Button b7=null;
public Button b8=null;
public Button b9=null;
public Button b10=null;
public Button b11=null;
public Button b12=null;
public Button b13=null;
public Button b14=null;
public Button b15=null;
public Button b16=null;
public Button b17=null;
public Button b18=null;
public Button b19=null;
public Button b20=null;
public Button b21=null;
public Button b22=null;
public Button b23=null;
public Button b24=null;
public Button b25=null;
public Button b26=null;
public Button b27=null;
public Button b28=null;
private double memNum=0;
private int operator=1;
private double num=0;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//setTheme(android.R.style.Theme_Black);
setContentView(R.layout.main);
reset();
t=(EditText)findViewById(R.id.editText1);
b1=(Button)findViewById(R.id.Button17);
b2=(Button)findViewById(R.id.Button18);
b3=(Button)findViewById(R.id.Button19);
b4=(Button)findViewById(R.id.Button12);
b5=(Button)findViewById(R.id.Button16);
b6=(Button)findViewById(R.id.Button15);
b7=(Button)findViewById(R.id.Button06);
b8=(Button)findViewById(R.id.Button05);
b9=(Button)findViewById(R.id.Button09);
b10=(Button)findViewById(R.id.button7);
b11=(Button)findViewById(R.id.button1);
b12=(Button)findViewById(R.id.button2);
b13=(Button)findViewById(R.id.button3);
b14=(Button)findViewById(R.id.Button11);
b15=(Button)findViewById(R.id.Button07);
b16=(Button)findViewById(R.id.Button01);
b17=(Button)findViewById(R.id.Button02);
b18=(Button)findViewById(R.id.Button03);
b19=(Button)findViewById(R.id.Button14);
b20=(Button)findViewById(R.id.button4);
b21=(Button)findViewById(R.id.Button10);
b22=(Button)findViewById(R.id.Button20);
b23=(Button)findViewById(R.id.button6);
b24=(Button)findViewById(R.id.button9);
b25=(Button)findViewById(R.id.button8);
b26=(Button)findViewById(R.id.Button13);
b27=(Button)findViewById(R.id.Button21);
b28=(Button)findViewById(R.id.button30);
b1.setOnClickListener(new Button.OnClickListener(){public void onClick(View v){handleNumber(1);}});
b2.setOnClickListener(new Button.OnClickListener(){public void onClick(View v){handleNumber(2);}});
b3.setOnClickListener(new Button.OnClickListener(){public void onClick(View v){handleNumber(3);}});
b4.setOnClickListener(new Button.OnClickListener(){public void onClick(View v){handleNumber(4);}});
b5.setOnClickListener(new Button.OnClickListener(){public void onClick(View v){handleNumber(5);}});
b6.setOnClickListener(new Button.OnClickListener(){public void onClick(View v){handleNumber(6);}});
b7.setOnClickListener(new Button.OnClickListener(){public void onClick(View v){handleNumber(7);}});
b8.setOnClickListener(new Button.OnClickListener(){public void onClick(View v){handleNumber(8);}});
b9.setOnClickListener(new Button.OnClickListener(){public void onClick(View v){handleNumber(9);}});
b10.setOnClickListener(new Button.OnClickListener(){public void onClick(View v){handleNumber(0);}});
b11.setOnClickListener(new Button.OnClickListener(){public void onClick(View v){memNum=0;}});
b12.setOnClickListener(new Button.OnClickListener(){public void onClick(View v){setValue(Double.toString(memNum));}});
b13.setOnClickListener(new Button.OnClickListener(){public void onClick(View v)
{}});
b14.setOnClickListener(new Button.OnClickListener(){public void onClick(View v){
memNum = memNum+ Double.parseDouble(t.getText().toString());
operator = 0;
}});
b15.setOnClickListener(new Button.OnClickListener(){public void onClick(View v){
memNum = memNum- Double.parseDouble(t.getText().toString());
operator = 0;
}});
b16.setOnClickListener(new Button.OnClickListener(){public void onClick(View v){handleBackspace();}});
b17.setOnClickListener(new Button.OnClickListener(){public void onClick(View v){}});
b18.setOnClickListener(new Button.OnClickListener(){public void onClick(View v){reset();}});
b19.setOnClickListener(new Button.OnClickListener(){public void onClick(View v){handlePlusMinus();}});
b20.setOnClickListener(new Button.OnClickListener(){public void onClick(View v){
setValue(Double.toString(Math.sqrt(Double.parseDouble(t.getText().toString()))));
}});
b21.setOnClickListener(new Button.OnClickListener(){public void onClick(View v){handleEquals(4);}});
b22.setOnClickListener(new Button.OnClickListener(){public void onClick(View v){handleEquals(3);}});
b23.setOnClickListener(new Button.OnClickListener(){public void onClick(View v){handleEquals(2);}});
b24.setOnClickListener(new Button.OnClickListener(){public void onClick(View v){handleEquals(1);}});
b25.setOnClickListener(new Button.OnClickListener(){public void onClick(View v){handleDecimal();}});
b26.setOnClickListener(new Button.OnClickListener(){public void onClick(View v){
setValue(Double.toString(num*(0.01 * Double.parseDouble(t.getText().toString()))));
}});
b27.setOnClickListener(new Button.OnClickListener(){public void onClick(View v){}});
b28.setOnClickListener(new Button.OnClickListener(){public void onClick(View v){handleEquals(0);}});
t.setOnKeyListener(new OnKeyListener()
{
public boolean onKey(View v,int i,android.view.KeyEvent e)
{
if (e.getAction() == KeyEvent.ACTION_DOWN)
{
int keyCode=e.getKeyCode();
switch (keyCode) {
case KeyEvent.KEYCODE_0:
handleNumber(0);
break;
case KeyEvent.KEYCODE_1:
handleNumber(1);
break;
case KeyEvent.KEYCODE_2:
handleNumber(2);
break;
case KeyEvent.KEYCODE_3:
handleNumber(3);
break;
case KeyEvent.KEYCODE_4:
handleNumber(4);
break;
case KeyEvent.KEYCODE_5:
handleNumber(5);
break;
case KeyEvent.KEYCODE_6:
handleNumber(6);
break;
case KeyEvent.KEYCODE_7:
handleNumber(7);
break;
case KeyEvent.KEYCODE_8:
handleNumber(8);
break;
case KeyEvent.KEYCODE_9:
handleNumber(9);
break;
case 43:
handleEquals(1);
break;
case KeyEvent.KEYCODE_EQUALS:
handleEquals(0);
break;
case KeyEvent.KEYCODE_MINUS:
handleEquals(2);
break;
case KeyEvent.KEYCODE_PERIOD:
handleDecimal();
break;
case KeyEvent.KEYCODE_C:
reset();
break;
case KeyEvent.KEYCODE_SLASH:
handleEquals(4);
break;
case KeyEvent.KEYCODE_DPAD_DOWN:
return false;
}
}
return true;
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
menu.add(0,1, MENUITEM_CLOSE, "Close");
return super.onCreateOptionsMenu(menu);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case MENUITEM_CLOSE:
finish();
break;
}
return super.onOptionsItemSelected(item);
}
private void handleEquals(int newOperator) {
if (hasChanged) {
switch (operator) {
case 1:
num = num + Double.parseDouble(t.getText().toString());
break;
case 2:
num = num - Double.parseDouble(t.getText().toString());
break;
case 3:
num = num * Double.parseDouble(t.getText().toString());
break;
case 4:
num = num / Double.parseDouble(t.getText().toString());
break;
}
String txt = Double.toString(num);
t.setText(txt);
t.setSelection(txt.length());
readyToClear = true;
hasChanged = false;
}
operator = newOperator;
}
private void handleNumber(int num) {
if (operator == 0)
reset();
String txt = t.getText().toString();
if (readyToClear) {
txt = "";
readyToClear = false;
} else if (txt.equals("0"))
txt = "";
txt = txt + Integer.toString(num);
t.setText(txt);
t.setSelection(txt.length());
hasChanged = true;
}
private void setValue(String value) {
if (operator == 0)
reset();
if (readyToClear) {
readyToClear = false;
}
t.setText(value);
t.setSelection(value.length());
hasChanged = true;
}
private void handleDecimal() {
if (operator == 0)
reset();
if (readyToClear) {
t.setText("0.");
t.setSelection(2);
readyToClear = false;
hasChanged = true;
} else {
String txt = t.getText().toString();
if (!txt.contains(".")) {
t.append(".");
hasChanged = true;
}
}
}
private void handleBackspace() {
if (!readyToClear) {
String txt = t.getText().toString();
if (txt.length() > 0) {
txt = txt.substring(0, txt.length() - 1);
if (txt.equals(""))
txt = "0";
t.setText(txt);
t.setSelection(txt.length());
}
}
}
private void handlePlusMinus() {
if (!readyToClear) {
String txt = t.getText().toString();
if (!txt.equals("0")) {
if (txt.charAt(0) == '-')
txt = txt.substring(1, txt.length());
else
txt = "-" + txt;
t.setText(txt);
t.setSelection(txt.length());
}
}
}
private void reset() {
num = 0;
t.setText("0");
t.setSelection(1);
operator = 1;
}
}