Android converting integer to string and string to integer

Question

I need that the each checkbox have own value like 1, 2 or 3, and u can check only 1 of first 3 checkboxes(cb1, cb2, cb3), and only 1 of second 3 checkboxes(cb4, cb5, cb6). But most imortant is to get summary of which checkboxes is cheked. App is crashing, what am I doing wrong? p.s. please excuse my bad English Here is the full source code:

public class MainActivity extends Activity {
    LinearLayout layout;
    Button bt;
    CheckBox cb1, cb2, cb3, cb4, cb5, cb6;
    TextView tv;
    String a, b, c;
    int d, e, f, g, h, i;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        layout = new LinearLayout(this);
        layout.setOrientation(LinearLayout.VERTICAL);
        cb1 = new CheckBox(this);
        cb2 = new CheckBox(this);
        cb3 = new CheckBox(this);
        cb4 = new CheckBox(this);
        cb5 = new CheckBox(this);
        cb6 = new CheckBox(this);
        bt = new Button(this);
        tv = new TextView(this);
        bt.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                a = "";
                b = "";
                c = "";
                d = 1;
                e = 2;
                f = 3;
                if (cb1.isChecked()){
                    a = Integer.toString(d);
                }else if (cb2.isChecked()){
                    a = Integer.toString(e);
                }else if (cb3.isChecked()){
                    a = Integer.toString(f);
                }else if (cb4.isChecked()){
                    b = Integer.toString(d);
                }else if (cb5.isChecked()){
                    b = Integer.toString(e);
                }else if (cb6.isChecked()){
                    b = Integer.toString(f);
                }
                g = Integer.valueOf(a);
                h = Integer.valueOf(b);
                i = g+h;
                c = Integer.toString(i);
                tv.setText(c);
            }
        });
        layout.addView(cb1);
        layout.addView(cb2);
        layout.addView(cb3);
        layout.addView(cb4);
        layout.addView(cb5);
        layout.addView(cb6);
        layout.addView(bt);
        layout.addView(tv);
        setContentView(layout);

    }
}

---

10-20 00:13:15.580: W/dalvikvm(2826): threadid=1: thread exiting with uncaught exception (group=0x40a71930)
10-20 00:13:15.700: E/AndroidRuntime(2826): FATAL EXCEPTION: main
10-20 00:13:15.700: E/AndroidRuntime(2826): java.lang.NullPointerException
10-20 00:13:15.700: E/AndroidRuntime(2826):     at com.example.test.MainActivity$1.onClick(MainActivity.java:58)
10-20 00:13:15.700: E/AndroidRuntime(2826):     at android.view.View.performClick(View.java:4204)
10-20 00:13:15.700: E/AndroidRuntime(2826):     at android.view.View$PerformClick.run(View.java:17355)
10-20 00:13:15.700: E/AndroidRuntime(2826):     at android.os.Handler.handleCallback(Handler.java:725)
10-20 00:13:15.700: E/AndroidRuntime(2826):     at android.os.Handler.dispatchMessage(Handler.java:92)
10-20 00:13:15.700: E/AndroidRuntime(2826):     at android.os.Looper.loop(Looper.java:137)
10-20 00:13:15.700: E/AndroidRuntime(2826):     at android.app.ActivityThread.main(ActivityThread.java:5041)
10-20 00:13:15.700: E/AndroidRuntime(2826):     at java.lang.reflect.Method.invokeNative(Native Method)
10-20 00:13:15.700: E/AndroidRuntime(2826):     at java.lang.reflect.Method.invoke(Method.java:511)
10-20 00:13:15.700: E/AndroidRuntime(2826):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
10-20 00:13:15.700: E/AndroidRuntime(2826):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
10-20 00:13:15.700: E/AndroidRuntime(2826):     at dalvik.system.NativeStart.main(Native Method)

Answer 1

These lines:

g = Integer.valueOf(a);
h = Integer.valueOf(b);

will give you an error in one of them because either a or b will always be equal to "" and you can't use Integer.valueOf(String) on an empty String.

To solve this problem, use this following code instead of those lines:

if (!a.equals(""))
    g = Integer.valueOf(a);
else
    g = 0;

if (!b.equals(""))
    h = Integer.valueOf(b);
else
    h = 0;

Answer 2

If none of your CheckBoxes are checked, a and b are "" (an empty String). So g = Integer.valueOf(a); and h = Integer.valueOf(b); must fail.