program stopped working in android Emulator

Question

I have written the program of calculator for android in Eclipse and no error was appeared while I was completing the codes but when the Emulator is running and for example entering two numbers to sum when the equation operator has clicked,this error appear "unfortunately app has stopped"

my Main.java

 package com.Tools.s01_e07; import android.app.Activity; import android.os.Bundle; import android.view.View; import android.view.View.OnClickListener; import android.widget.ImageView; import android.widget.TextView; public class Main extends Activity { private TextView show; private ImageView n1; private ImageView n2; private ImageView n3; private ImageView n4; private ImageView n5; private ImageView n6; private ImageView n7; private ImageView n8; private ImageView n9; private ImageView n0; private ImageView nf1; private ImageView nf2; private ImageView nf3; private ImageView nf4; private ImageView nf5; private ImageView nf6; private int V1; private String F; private int V2; protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); n1=(ImageView) findViewById(R.id.n1); n2=(ImageView) findViewById(R.id.n2); n3=(ImageView) findViewById(R.id.n3); n4=(ImageView) findViewById(R.id.n4); n5=(ImageView) findViewById(R.id.n5); n6=(ImageView) findViewById(R.id.n6); n7=(ImageView) findViewById(R.id.n7); n8=(ImageView) findViewById(R.id.n8); n9=(ImageView) findViewById(R.id.n9); n0=(ImageView) findViewById(R.id.n0); nf1=(ImageView) findViewById(R.id.nf1); nf2=(ImageView) findViewById(R.id.nf2); nf3=(ImageView) findViewById(R.id.nf3); nf4=(ImageView) findViewById(R.id.nf4); nf5=(ImageView) findViewById(R.id.nf5); nf6=(ImageView) findViewById(R.id.nf6); show=(TextView) findViewById(R.id.show); n1.setOnClickListener(new OnClickListener() { public void onClick(View arg0) { show.setText(show.getText()+"1"); } }); n2.setOnClickListener(new OnClickListener() { public void onClick(View arg0) { show.setText(show.getText()+"2"); } }); n3.setOnClickListener(new OnClickListener() { public void onClick(View arg0) { show.setText(show.getText()+"3"); } }); n4.setOnClickListener(new OnClickListener() { public void onClick(View arg0) { show.setText(show.getText()+"4"); } }); n5.setOnClickListener(new OnClickListener() { public void onClick(View arg0) { show.setText(show.getText()+"5"); } }); n6.setOnClickListener(new OnClickListener() { public void onClick(View arg0) { show.setText(show.getText()+"6"); } }); n7.setOnClickListener(new OnClickListener() { public void onClick(View arg0) { show.setText(show.getText()+"7"); } }); n8.setOnClickListener(new OnClickListener() { public void onClick(View arg0) { show.setText(show.getText()+"8"); } }); n9.setOnClickListener(new OnClickListener() { public void onClick(View arg0) { show.setText(show.getText()+"9"); } }); n0.setOnClickListener(new OnClickListener() { public void onClick(View arg0) { show.setText(show.getText()+"0"); } }); nf1.setOnClickListener(new OnClickListener() { public void onClick(View arg0) { V1=Integer.parseInt(show.getText().toString()); F="+"; show.setText(" "); } }); nf2.setOnClickListener(new OnClickListener() { public void onClick(View arg0) { V1=Integer.parseInt(show.getText().toString()); F="-"; show.setText(" "); } }); nf3.setOnClickListener(new OnClickListener() { public void onClick(View arg0) { V1=Integer.parseInt(show.getText().toString()); F="*"; show.setText(" "); } }); nf4.setOnClickListener(new OnClickListener() { public void onClick(View arg0) { V1=Integer.parseInt(show.getText().toString()); F="/"; show.setText(" "); } }); nf5.setOnClickListener(new OnClickListener() { public void onClick(View arg0) { if(F!="" && show.getText().toString()!="") { int res=0; V2=Integer.parseInt(show.getText().toString()); if(F=="+"){ res=V1+V2; } if(F=="-"){ res=V1-V2; } if(F=="*"){ res=V1*V2; } if(F=="/"){ res=V1/V2; } show.setText(res+""); } } }); nf6.setOnClickListener(new OnClickListener() { public void onClick(View arg0) { } }); } } 

main.xml

 <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" android:paddingBottom="@dimen/activity_vertical_margin" android:paddingLeft="@dimen/activity_horizontal_margin" android:paddingRight="@dimen/activity_horizontal_margin" android:paddingTop="@dimen/activity_vertical_margin" tools:context="com.Tools.s01_e07.Main" > <ImageView android:id="@+id/n1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_alignParentBottom="true" android:layout_alignParentLeft="true" android:layout_marginBottom="116dp" android:layout_marginLeft="64dp" android:src="@drawable/a01" /> <ImageView android:id="@+id/n2" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_alignTop="@+id/n1" android:layout_toRightOf="@+id/n1" android:src="@drawable/a02" /> <ImageView android:id="@+id/n3" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_alignTop="@+id/n2" android:layout_toRightOf="@+id/n2" android:src="@drawable/a03" /> <ImageView android:id="@+id/n4" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_above="@+id/n1" android:layout_alignLeft="@+id/n1" android:src="@drawable/a04" /> <ImageView android:id="@+id/n5" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_above="@+id/n1" android:layout_toRightOf="@+id/n1" android:src="@drawable/a05" /> <ImageView android:id="@+id/n6" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_alignLeft="@+id/n3" android:layout_alignTop="@+id/n5" android:src="@drawable/a06" /> <ImageView android:id="@+id/n7" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_above="@+id/n4" android:layout_alignLeft="@+id/n4" android:src="@drawable/a07" /> <ImageView android:id="@+id/n8" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_alignTop="@+id/n7" android:layout_toRightOf="@+id/n7" android:src="@drawable/a08" /> <ImageView android:id="@+id/n9" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_alignLeft="@+id/n6" android:layout_alignTop="@+id/n8" android:src="@drawable/a09" /> <ImageView android:id="@+id/n0" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_below="@+id/n2" android:layout_toRightOf="@+id/n1" android:src="@drawable/a00" /> <ImageView android:id="@+id/nf5" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_below="@+id/n2" android:layout_toRightOf="@+id/n2" android:src="@drawable/mosavi" /> <ImageView android:id="@+id/nf1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_alignTop="@+id/n9" android:layout_toRightOf="@+id/n9" android:src="@drawable/sum" /> <ImageView android:id="@+id/nf2" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_alignLeft="@+id/nf1" android:layout_below="@+id/nf1" android:src="@drawable/tafrigh" /> <ImageView android:id="@+id/nf3" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_below="@+id/nf2" android:layout_toRightOf="@+id/n3" android:src="@drawable/zarb" /> <ImageView android:id="@+id/nf4" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_alignRight="@+id/nf3" android:layout_below="@+id/nf3" android:src="@drawable/taghsim" /> <ImageView android:id="@+id/nf6" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_alignLeft="@+id/n1" android:layout_alignTop="@+id/nf4" android:src="@drawable/p2" /> <TextView android:id="@+id/show" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_above="@+id/n7" android:layout_alignLeft="@+id/n7" android:layout_alignRight="@+id/nf1" android:layout_marginBottom="40dp" android:textAppearance="?android:attr/textAppearanceMedium" android:textSize="22sp" /> </RelativeLayout> 

this is my LogCat

 03-20 14:59:37.211: D/dalvikvm(1225): GC_CONCURRENT freed 69K, 5% free 6286K/6616K, paused 3ms+2ms, total 26ms 03-20 14:59:37.283: D/libEGL(1225): loaded /system/lib/egl/libEGL_genymotion.so 03-20 14:59:37.287: D/(1225): HostConnection::get() New Host Connection established 0xb78f8410, tid 1225 03-20 14:59:37.299: D/libEGL(1225): loaded /system/lib/egl/libGLESv1_CM_genymotion.so 03-20 14:59:37.299: D/libEGL(1225): loaded /system/lib/egl/libGLESv2_genymotion.so 03-20 14:59:37.355: W/EGL_genymotion(1225): eglSurfaceAttrib not implemented 03-20 14:59:37.367: D/OpenGLRenderer(1225): Enabling debug mode 0 03-20 15:00:01.239: D/AndroidRuntime(1225): Shutting down VM 03-20 15:00:01.239: W/dalvikvm(1225): threadid=1: thread exiting with uncaught exception (group=0xa613f908) 03-20 15:00:01.239: E/AndroidRuntime(1225): FATAL EXCEPTION: main 03-20 15:00:01.239: E/AndroidRuntime(1225): java.lang.NumberFormatException: Invalid int: " 2" 03-20 15:00:01.239: E/AndroidRuntime(1225): at java.lang.Integer.invalidInt(Integer.java:138) 03-20 15:00:01.239: E/AndroidRuntime(1225): at java.lang.Integer.parse(Integer.java:375) 03-20 15:00:01.239: E/AndroidRuntime(1225): at java.lang.Integer.parseInt(Integer.java:366) 03-20 15:00:01.239: E/AndroidRuntime(1225): at java.lang.Integer.parseInt(Integer.java:332) 03-20 15:00:01.239: E/AndroidRuntime(1225): at com.Tools.s01_e07.Main$15.onClick(Main.java:173) 03-20 15:00:01.239: E/AndroidRuntime(1225): at android.view.View.performClick(View.java:4204) 03-20 15:00:01.239: E/AndroidRuntime(1225): at android.view.View$PerformClick.run(View.java:17355) 03-20 15:00:01.239: E/AndroidRuntime(1225): at android.os.Handler.handleCallback(Handler.java:725) 03-20 15:00:01.239: E/AndroidRuntime(1225): at android.os.Handler.dispatchMessage(Handler.java:92) 03-20 15:00:01.239: E/AndroidRuntime(1225): at android.os.Looper.loop(Looper.java:137) 03-20 15:00:01.239: E/AndroidRuntime(1225): at android.app.ActivityThread.main(ActivityThread.java:5041) 03-20 15:00:01.239: E/AndroidRuntime(1225): at java.lang.reflect.Method.invokeNative(Native Method) 03-20 15:00:01.239: E/AndroidRuntime(1225): at java.lang.reflect.Method.invoke(Method.java:511) 03-20 15:00:01.239: E/AndroidRuntime(1225): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 03-20 15:00:01.239: E/AndroidRuntime(1225): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) 03-20 15:00:01.239: E/AndroidRuntime(1225): at dalvik.system.NativeStart.main(Native Method) 

Answer 1

When an operator button is pressed, you set the show TextView to " " (space) and then append the digits of the second operator to it. You probably get a NumberFormatException in parseInt. You should also not trust the user clicking the buttons as they normally should.