My calculator program just doesnt seem to work. It crashes everytime i click on a number button. Please help.Thanks in advance
The logcat report:
01-17 16:08:46.949: D/AndroidRuntime(321): Shutting down VM
01-17 16:08:46.949: W/dalvikvm(321): threadid=1: thread exiting with uncaught exception (group=0x4001d800)
01-17 16:08:46.969: E/AndroidRuntime(321): FATAL EXCEPTION: main
01-17 16:08:46.969: E/AndroidRuntime(321): java.lang.NullPointerException
01-17 16:08:46.969: E/AndroidRuntime(321): at net.learn.calc.CalciActivity.handlenumber(CalciActivity.java:189)
01-17 16:08:46.969: E/AndroidRuntime(321): at net.learn.calc.CalciActivity$9.onClick(CalciActivity.java:110)
01-17 16:08:46.969: E/AndroidRuntime(321): at android.view.View.performClick(View.java:2408)
01-17 16:08:46.969: E/AndroidRuntime(321): at android.view.View$PerformClick.run(View.java:8816)
01-17 16:08:46.969: E/AndroidRuntime(321): at android.os.Handler.handleCallback(Handler.java:587)
01-17 16:08:46.969: E/AndroidRuntime(321): at android.os.Handler.dispatchMessage(Handler.java:92)
01-17 16:08:46.969: E/AndroidRuntime(321): at android.os.Looper.loop(Looper.java:123)
01-17 16:08:46.969: E/AndroidRuntime(321): at android.app.ActivityThread.main(ActivityThread.java:4627)
01-17 16:08:46.969: E/AndroidRuntime(321): at java.lang.reflect.Method.invokeNative(Native Method)
01-17 16:08:46.969: E/AndroidRuntime(321): at java.lang.reflect.Method.invoke(Method.java:521)
01-17 16:08:46.969: E/AndroidRuntime(321): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
01-17 16:08:46.969: E/AndroidRuntime(321): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
01-17 16:08:46.969: E/AndroidRuntime(321): at dalvik.system.NativeStart.main(Native Method)
here’s the program:
package net.learn.calc;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
public class CalciActivity extends Activity {
/** Called when the activity is first created. */
EditText ent=null;
Button a,b,c,d,e,f,g,h,i,j,add,sub,mul,div,equ,dot,cl,del;
double num=0;
int operator=1;
boolean clearrdy=false;
boolean numbpre=false;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
a=(Button)findViewById(R.id.zero);
b=(Button)findViewById(R.id.one);
c=(Button)findViewById(R.id.two);
d=(Button)findViewById(R.id.three);
e=(Button)findViewById(R.id.four);
f=(Button)findViewById(R.id.five);
g=(Button)findViewById(R.id.six);
h=(Button)findViewById(R.id.seven);
i=(Button)findViewById(R.id.eight);
j=(Button)findViewById(R.id.nine);
add=(Button)findViewById(R.id.plus);
sub=(Button)findViewById(R.id.minus);
mul=(Button)findViewById(R.id.multiply);
div=(Button)findViewById(R.id.divide);
equ=(Button)findViewById(R.id.equal);
dot=(Button)findViewById(R.id.decimal);
cl=(Button)findViewById(R.id.clear);
del=(Button)findViewById(R.id.delete);
a.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
handlenumber(0);
}
});
b.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
handlenumber(1);
}
});
c.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
handlenumber(2);
}
});
d.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
handlenumber(3);
}
});
e.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
handlenumber(4);
}
});
f.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
handlenumber(5);
}
});
g.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
handlenumber(6);
}
});
h.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
handlenumber(7);
}
});
i.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
handlenumber(8);
}
});
j.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
handlenumber(9);
}
});
add.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
handleop(1);
}
});
sub.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
handleop(2);
}
});
mul.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
handleop(3);
}
});
div.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
handleop(4);
}
});
equ.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
handleop(0);
}
});
dot.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
handledecimal();
}
});
cl.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
reset1();
}
});
del.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
backsp1();
}
});
}
public void handlenumber(int n)
{
String str=ent.getText().toString();
if(clearrdy)
{
str="";
clearrdy=false;
}
String val=Integer.toString(n);
str=str+val;
ent.setText(str);
ent.setSelection(str.length());
numbpre=true;
}
public void handledecimal()
{ String str=ent.getText().toString();
if(clearrdy)
{
str="0.";
}
else
{
str=str+".";
}
ent.setText(str);
ent.setSelection(str.length());
clearrdy=false;
numbpre=true;
}
public void handleop(int newop)
{
if(numbpre)
{
switch(operator)
{
case 1:
num=num + Double.parseDouble(ent.getText().toString());
break;
case 2:
num=num - Double.parseDouble(ent.getText().toString());
break;
case 3:
num=num * Double.parseDouble(ent.getText().toString());
break;
case 4:
num=num/Double.parseDouble(ent.getText().toString());
break;
}
}
String str=Double.toString(num);
ent.setText(str);
ent.setSelection(str.length());
numbpre=false;
clearrdy=true;
operator=newop;
}
public void reset1()
{
numbpre=false;
clearrdy=false;
operator=1;
num=0;
}
public void backsp1()
{
String str=ent.getText().toString();
if (str.length() > 0) {
str=str.substring(0,str.length() - 1);
ent.setText(str);
ent.setSelection(str.length());
}
}
}
<?xml version="1.0" encoding="utf-8"?>
<AbsoluteLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<EditText
android:id="@+id/entry"
android:layout_width="fill_parent"
android:layout_height="84dp"
android:layout_x="0dp"
android:layout_y="29dp" >
<requestFocus />
</EditText>
<Button
android:id="@+id/equal"
android:layout_width="58dp"
android:layout_height="72dp"
android:layout_x="250dp"
android:layout_y="407dp"
android:text="=" />
<Button
android:id="@+id/divide"
android:layout_width="58dp"
android:layout_height="72dp"
android:layout_x="180dp"
android:layout_y="403dp"
android:text="/" />
<Button
android:id="@+id/multiply"
android:layout_width="58dp"
android:layout_height="72dp"
android:layout_x="250dp"
android:layout_y="324dp"
android:text="X" />
<Button
android:id="@+id/nine"
android:layout_width="58dp"
android:layout_height="72dp"
android:layout_x="176dp"
android:layout_y="322dp"
android:text="9" />
<Button
android:id="@+id/seven"
android:layout_width="58dp"
android:layout_height="72dp"
android:layout_x="38dp"
android:layout_y="322dp"
android:text="7" />
<Button
android:id="@+id/eight"
android:layout_width="58dp"
android:layout_height="72dp"
android:layout_x="107dp"
android:layout_y="322dp"
android:text="8" />
<Button
android:id="@+id/zero"
android:layout_width="58dp"
android:layout_height="72dp"
android:layout_x="107dp"
android:layout_y="403dp"
android:text="0" />
<Button
android:id="@+id/decimal"
android:layout_width="58dp"
android:layout_height="72dp"
android:layout_x="36dp"
android:layout_y="403dp"
android:text="." />
<Button
android:id="@+id/five"
android:layout_width="58dp"
android:layout_height="72dp"
android:layout_x="105dp"
android:layout_y="247dp"
android:text="5" />
<Button
android:id="@+id/four"
android:layout_width="58dp"
android:layout_height="72dp"
android:layout_x="36dp"
android:layout_y="243dp"
android:text="4" />
<Button
android:id="@+id/six"
android:layout_width="58dp"
android:layout_height="72dp"
android:layout_x="174dp"
android:layout_y="247dp"
android:text="6" />
<Button
android:id="@+id/minus"
android:layout_width="58dp"
android:layout_height="72dp"
android:layout_x="246dp"
android:layout_y="245dp"
android:text="-" />
<Button
android:id="@+id/three"
android:layout_width="58dp"
android:layout_height="72dp"
android:layout_x="174dp"
android:layout_y="168dp"
android:text="3" />
<Button
android:id="@+id/two"
android:layout_width="59dp"
android:layout_height="72dp"
android:layout_x="104dp"
android:layout_y="168dp"
android:text="2" />
<Button
android:id="@+id/one"
android:layout_width="57dp"
android:layout_height="70dp"
android:layout_x="40dp"
android:layout_y="168dp"
android:text="1" />
<Button
android:id="@+id/plus"
android:layout_width="58dp"
android:layout_height="72dp"
android:layout_x="244dp"
android:layout_y="170dp"
android:text="+" />
<Button
android:id="@+id/delete"
android:layout_width="88dp"
android:layout_height="wrap_content"
android:layout_x="194dp"
android:layout_y="116dp"
android:text="DEL" />
<Button
android:id="@+id/clear"
android:layout_width="84dp"
android:layout_height="wrap_content"
android:layout_x="66dp"
android:layout_y="118dp"
android:text="C" />
</AbsoluteLayout>
From what I can see, you don’t assign
entto any control (all you have isEditText ent=null;), so you get a null error when calling: