My Simple Interest calculator is crashing with a null pointer exception error

My Simple Interest calculator is crashing with a null pointer exception error, not sure what the problem is, there are no errors in the IDE before I complile, this is new to me. Here is my code and logcat: edit: Icouldn't post a logcat as the editor thinks it's code and I can't get it to format correctly Code:

package com.codeherenow.sicalculator;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.SeekBar;

public class SICalculatorActivity extends Activity
    implements SeekBar.OnSeekBarChangeListener, View.OnClickListener{
private int years;
private TextView YT;
private SeekBar bar;
private EditText principal = (EditText) findViewById(R.id.PA_field);
private EditText interest = (EditText) findViewById(R.id.IR_field);
public EditText pvalue;
public EditText ivalue;
private double mPvalue = 0;
private double mIvalue = 0;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.sicalculator);
    bar = (SeekBar)findViewById(R.id.seekBar);
    bar.setOnSeekBarChangeListener(this);
    pvalue = (EditText) principal.getText();
    ivalue = (EditText) interest.getText();
    String s = principal.getText().toString();
    mPvalue = Double.parseDouble(s);
    String s2 = interest.getText().toString();
    mIvalue = Double.parseDouble(s2);

}
    @Override
    public void onProgressChanged (SeekBar seekBar,int i, boolean b){
        years = i;
        YT = (TextView) findViewById(R.id.Years);
        YT.setText(years + " Year(s)");

    }

    @Override
    public void onStartTrackingTouch (SeekBar seekBar){

    }

    @Override
    public void onStopTrackingTouch (SeekBar seekBar){

    }

@Override
public void onClick(View view) {
    TextView fTextView = (TextView) findViewById(R.id.finalText);
    double finValue = mPvalue * (mIvalue/100) * years;
    fTextView.setText("The interest for " + pvalue + "at a rate of " +    ivalue + "for " + years + "year(s) is " + finValue);
}
}