Null pointer exception with values on text change listener android

I have code to simply calculate compound interest. The calculation will change when the user edits the value in an EditText view.

public class CompoundInterest extends AppCompatActivity {

    TextView mCompBalance;
    TextView mBalance;
    EditText mYears;
    Integer balance;
    Integer years;
    Double compbalance;
    Double interest;
    boolean isNumber;



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_compound_interest);

        interest = 0.025;

        mBalance = (TextView) findViewById(R.id.tv_savingsbalance);
        mCompBalance = (TextView) findViewById(R.id.tv_interestbalance);
        mYears = (EditText) findViewById(R.id.et_years);
        System.out.println(mYears.getText().toString());

        Resources res = getResources();
        balance = Integer.valueOf(res.getString(R.string.savings_balance));
        mBalance.setText("£"+ balance);


        mYears.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {

            }

            @Override
            public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {
                if (mYears.getText().toString().matches("\\d+(?:\\.\\d+)?")){
                    years = Integer.valueOf(mYears.getText().toString());
                    System.out.println(years);
                    isNumber =true;
                } else {
                    isNumber =false;
                }

                if (isNumber){
                    compbalance = balance*Math.pow(1+interest, years);
                    mCompBalance.setText("£"+String.format("%.2f", compbalance));
                }

            }

            @Override
            public void afterTextChanged(Editable editable) {

            }
        });


    }
}

When I try to edit the EditText view that sets the number of years for the calculation - I get this error and the app crashes:

java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.Integer.intValue()' on a null object reference at com.###.android.citiapp.CompoundInterest$1.onTextChanged(CompoundInterest.java:63) at android.widget.TextView.sendOnTextChanged(TextView.java:8187) at android.widget.TextView.handleTextChanged(TextView.java:8249) at android.widget.TextView$ChangeWatcher.onTextChanged(TextView.java:10371) at android.text.SpannableStringBuilder.sendTextChanged(SpannableStringBuilder.java:1208) at android.text.SpannableStringBuilder.replace(SpannableStringBuilder.java:578) at android.text.SpannableStringBuilder.delete(SpannableStringBuilder.java:230) at android.text.SpannableStringBuilder.delete(SpannableStringBuilder.java:229) at android.view.inputmethod.BaseInputConnection.deleteSurroundingText(BaseInputConnection.java:251) at com.android.internal.view.IInputConnectionWrapper.executeMessage(IInputConnectionWrapper.java:459) at com.android.internal.view.IInputConnectionWrapper$MyHandler.handleMessage(IInputConnectionWrapper.java:93) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:154) at android.app.ActivityThread.main(ActivityThread.java:6119) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

I'm not sure what's going on.

Use charSequence.toString() instead of mYears.getText().toString() in onTextChanged function. Hope it helps or specify exactly where NullPointerException is occurring?