the Android can not find the class of the external pot


I am trying to create a simple test app that basically extends the Android Hello World tutorial app by invoking some simple functionality from an external JAR. However, when I run the app, it can't find the class from the JAR. What am I doing wrong?

Here's entire source of the JAR:

package com.mytests.pow;

public class power2 {

private double d;   

public power2()
    d = 0.0;

public String stp2(double dd)
    d = dd*dd;
    return String.format("%e", d);


And here's the "Hello World ++" source:

package com.myLuceneTests.namespace;

import android.os.Bundle;
import android.widget.TextView;

import com.mytests.pow.*;

public class AndroidSimpleSIH_EclipseActivity extends Activity {
/** Called when the activity is first created. */
public void onCreate(Bundle savedInstanceState) {

    power2 pp = new power2();
    String iout = pp.stp2(12.0);

    TextView tv = new TextView(this);


When I run the app, I get this in logcat:

11-22 12:24:52.697  2963  2963 E dalvikvm: Could not find class 'com.mytests.pow.power2', referenced from method com.myLuceneTests.namespace


and then

11-22 12:24:52.713  2963  2963 E AndroidRuntime: java.lang.NoClassDefFoundError: com.mytests.pow.power2

What am I doing wrong? Thanks!

By the way, my actual goal is to use a real JAR (rather than this toy one) in an Android app. I might have access to the code for that JAR and might be able to rebuild it but it's a big piece of Java code and I am likely to encounter problems when rebuilding it so I am trying to use the pre-built JAR.

There's no need to build the external jar. Try removing it from your build path and follow these steps:

  1. Create a folder in the root of your Android project called libs.
  2. Add the jar to that folder.
  3. Right-click the jar and click to add to build path.
  4. Clean your project and try it again.