Question

I’m pretty new to Java and Android. I’m trying to make an app that calculates a volume of a liquid in a cylinder, then return the result to a textView box. But now when I click the button to Calculate, it is crashing and I don’t know what I’m missing. Everything compiles fine.

package com.somename.fuel.volume.calculator;

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

public class CalculateCylinder extends Activity {

EditText length, width, height, depth;
TextView result;
Button calculate;
double firstNum, secNum, thirdNum, volume, area;
double liqVolume;
double radius;
double a, l, aSide,aTop,b,Arc,FluidSurfaceAreaTotal,r,d,v,h,fsal;

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.calculate_cylinder);

    calculate = (Button) findViewById(R.id.buttonCylCalc);

    length = (EditText) findViewById(R.id.editCylLength);
    height = (EditText) findViewById(R.id.editCylHeight);
    depth = (EditText) findViewById(R.id.editCylDepth);
    result = (TextView) findViewById(R.id.buttonCylResult);

    calculate.setOnClickListener(new View.OnClickListener() {

        public void onClick(View v) {
            // TODO Auto-generated method stub
            //Toast.makeText(getApplicationContext(), (CharSequence) result, Toast.LENGTH_LONG).show();
            try {
                calculate();
            } catch (Exception e) {
                e.printStackTrace();
            }
            result.setText((CharSequence) result);
        }

        public TextView calculate() throws Exception {
            // TODO Auto-generated method stub
            double firstNum = Double.valueOf(length.getText().toString());
            double secNum   = Double.valueOf(height.getText().toString());
            double thirdNum = Double.valueOf(depth.getText().toString());

            radius = (secNum/2);
            area = ((secNum*secNum)*3.14);
            //liqVolume = (firstNum) * (radius*radius)(acos(radius-depth/radius))
            // Cubic Volume

            v = aSide * l;
            // Fluid surface Area, Side
            aSide = (r*r)*(3.14 / 2 -Math.acos(1-h/r)) - (r-h)*Math.sqrt(h*(2*r-h));
            // Fluid Surface Area Top
            aTop = 2*Math.sqrt((r*r)-((r-h)*(r-h) * l));
            // Fluid Surface Area Bottom
            b = fsal*l;
            // Fluid Surface Area Total
            FluidSurfaceAreaTotal = 2*aSide+aTop+b;
            // Cylinder Radius
            r = d/2;
            // Cylinder Diameter
            d = 2*r;
            if (h <= r )
                // Fluid Side Arc Length
                fsal = 2*r*Math.acos((r-h)/r);

            else if (h > r)
                fsal = 2*r*(3.14-Math.acos((h-r)/r));
            return result;
            }


    });
}   

}

Here is a logcat:

10-18 05:24:38.893: E/AndroidRuntime(964): FATAL EXCEPTION: main
10-18 05:24:38.893: E/AndroidRuntime(964): java.lang.ClassCastException:    android.widget.Button
10-18 05:24:38.893: E/AndroidRuntime(964):  at   com.dbryant423.fuel.volume.calculator.CalculateCylinder$1.onClick(CalculateCylinder.java:55 )
10-18 05:24:38.893: E/AndroidRuntime(964):  at android.view.View.performClick(View.java:2408)
10-18 05:24:38.893: E/AndroidRuntime(964):  at android.view.View$PerformClick.run(View.java:8816)
10-18 05:24:38.893: E/AndroidRuntime(964):  at android.os.Handler.handleCallback(Handler.java:587)
10-18 05:24:38.893: E/AndroidRuntime(964):  at android.os.Handler.dispatchMessage(Handler.java:92)
10-18 05:24:38.893: E/AndroidRuntime(964):  at android.os.Looper.loop(Looper.java:123)
10-18 05:24:38.893: E/AndroidRuntime(964):  at android.app.ActivityThread.main(ActivityThread.java:4627)
10-18 05:24:38.893: E/AndroidRuntime(964):  at java.lang.reflect.Method.invokeNative(Native Method)
10-18 05:24:38.893: E/AndroidRuntime(964):  at java.lang.reflect.Method.invoke(Method.java:521)
10-18 05:24:38.893: E/AndroidRuntime(964):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
10-18 05:24:38.893: E/AndroidRuntime(964):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
10-18 05:24:38.893: E/AndroidRuntime(964):  at dalvik.system.NativeStart.main(Native Method)

I’ve been wracking my brains to try to figure out how to do the math on this, and I’ve not been able to find the answer to why it’s crashing. I’m sure it’s probably something simple that I’ve missed somewhere. If you need more information from the other files let me know, but this one seem the be the only one with the problem. I also know that there is unused variables that I’ve not removed yet.

Answer 1

result.setText((CharSequence) result);

This line cause Exception because you are casting Android View class to CharSequence Class.

Possible Solution:

Change return type of your method public TextView calculate() to

public String calculate()

Now in method public String calculate() return String of result fsal

And your button’s Click() is something like,

calculate.setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {
            // TODO Auto-generated method stub
            //Toast.makeText(getApplicationContext(), (CharSequence) result, Toast.LENGTH_LONG).show();
           String resultValue = "";
            try {
             resultValue =  calculate();
            } catch (Exception e) {
                e.printStackTrace();
            }
            result.setText( resultValue);
        }