if (a=="" && b=="")

并且也在线

int result = Integer.parseInt(a) + Integer.parseInt(b);
 t1.setText(Integer.toString(result));

Calci.java

package com.example.calculator;

import android.app.Activity;
import android.app.AlertDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.os.Bundle;
import android.view.View;
import android.view.inputmethod.InputMethodManager;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class Calci extends Activity {
    TextView t1;
    EditText e1,e2;
    Button add,sub,mul,div;
    Context c=this;

    String b,a;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_calci);
        e1 = (EditText) findViewById(R.id.EditText01);
        e2 = (EditText) findViewById(R.id.EditText02);
        add = (Button) findViewById(R.id.add);
        sub = (Button) findViewById(R.id.sub);
        mul = (Button) findViewById(R.id.mul);
        div = (Button) findViewById(R.id.div);
        t1 = (TextView) findViewById(R.id.textView1);
        a = e1.getText().toString();
        b = e2.getText().toString();
add.setOnClickListener(new View.OnClickListener() {

    @Override
    public void onClick(View arg0) {
        if (a=="" && b==""){
                AlertDialog.Builder a1 = new AlertDialog.Builder(c);


                // Setting Dialog Title
                a1.setTitle("Alert Dialog");

                // Setting Dialog Message
                a1.setMessage("PLEASE ENTER SOMETHING");

                a1.setPositiveButton("yes",new DialogInterface.OnClickListener() {
                            public void onClick(DialogInterface dialog,int button1) {
                                // if this button is clicked,close
                                // current activity
                                dialog.cancel();
                            }

                        });

                // Showing Alert Message
                AlertDialog alertDialog = a1.create();
                a1.show();

            }

        else{
            int result = Integer.parseInt(a) + Integer.parseInt(b);
            t1.setText(Integer.toString(result));
            InputMethodManager imm = (InputMethodManager)getSystemService(
                      Context.INPUT_METHOD_SERVICE);
                imm.hideSoftInputFromWindow(add.getWindowToken(),0);
        }

    }

});
    }
}

logcat的：

03-19 15:42:21.165: E/Trace(25381): error opening trace file: Permission denied (13)
03-19 15:42:21.165: D/ActivityThread(25381): setTargetHeapUtilization:0.25
03-19 15:42:21.165: D/ActivityThread(25381): setTargetHeapIdealFree:8388608
03-19 15:42:21.165: D/ActivityThread(25381): setTargetHeapConcurrentStart:2097152
03-19 15:42:21.385: D/libEGL(25381): loaded /system/lib/egl/libEGL_adreno200.so
03-19 15:42:21.465: D/libEGL(25381): loaded /system/lib/egl/libGLESv1_CM_adreno200.so
03-19 15:42:21.475: D/libEGL(25381): loaded /system/lib/egl/libGLESv2_adreno200.so
03-19 15:42:21.475: I/Adreno200-EGL(25381): <qeglDrvAPI_eglInitialize:299>: EGL 1.4 QUALCOMM build:  (Merge)
03-19 15:42:21.475: I/Adreno200-EGL(25381): Build Date: 07/09/13 Tue
03-19 15:42:21.475: I/Adreno200-EGL(25381): Local Branch: AU_41
03-19 15:42:21.475: I/Adreno200-EGL(25381): Remote Branch: 
03-19 15:42:21.475: I/Adreno200-EGL(25381): Local Patches: 
03-19 15:42:21.475: I/Adreno200-EGL(25381): Reconstruct Branch: 
03-19 15:42:21.675: D/OpenGLRenderer(25381): Enabling debug mode 0
03-19 15:42:24.325: D/AndroidRuntime(25381): Shutting down VM
03-19 15:42:24.325: W/dalvikvm(25381): threadid=1: thread exiting with uncaught exception (group=0x41972378)
03-19 15:42:24.395: E/AndroidRuntime(25381): FATAL EXCEPTION: main
03-19 15:42:24.395: E/AndroidRuntime(25381): java.lang.NumberFormatException: Invalid int: ""
03-19 15:42:24.395: E/AndroidRuntime(25381):    at java.lang.Integer.invalidInt(Integer.java:138)
03-19 15:42:24.395: E/AndroidRuntime(25381):    at java.lang.Integer.parseInt(Integer.java:359)
03-19 15:42:24.395: E/AndroidRuntime(25381):    at java.lang.Integer.parseInt(Integer.java:332)
03-19 15:42:24.395: E/AndroidRuntime(25381):    at com.example.calculator.Calci$1.onClick(Calci.java:67)
03-19 15:42:24.395: E/AndroidRuntime(25381):    at android.view.View.performClick(View.java:4147)
03-19 15:42:24.395: E/AndroidRuntime(25381):    at android.view.View$PerformClick.run(View.java:17161)
03-19 15:42:24.395: E/AndroidRuntime(25381):    at android.os.Handler.handleCallback(Handler.java:615)
03-19 15:42:24.395: E/AndroidRuntime(25381):    at android.os.Handler.dispatchMessage(Handler.java:92)
03-19 15:42:24.395: E/AndroidRuntime(25381):    at android.os.Looper.loop(Looper.java:213)
03-19 15:42:24.395: E/AndroidRuntime(25381):    at android.app.ActivityThread.main(ActivityThread.java:4787)
03-19 15:42:24.395: E/AndroidRuntime(25381):    at java.lang.reflect.Method.invokeNative(Native Method)
03-19 15:42:24.395: E/AndroidRuntime(25381):    at java.lang.reflect.Method.invoke(Method.java:511)
03-19 15:42:24.395: E/AndroidRuntime(25381):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789)
03-19 15:42:24.395: E/AndroidRuntime(25381):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:556)
03-19 15:42:24.395: E/AndroidRuntime(25381):    at dalvik.system.NativeStart.main(Native Method)
03-19 15:42:25.685: I/Process(25381): Sending signal. PID: 25381 SIG: 9

任何人都知道如何解决这些堆栈跟踪错误.

解决方法

a = e1.getText().toString().trim();    
 b = e2.getText().toString().trim(); 
 if (a.equals("") && b.equals("") ){

 }

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