title: Android: cannot access java.lang.AbstractStringBuilder
body: <p>I have a StringBuilder argument passed to another module's class method and do some modification, include deleteCharAt, clear, append..., etc.</p>
  
  <p>I got following warning message in Android Studio though the code seems run very well.</p>
  
  <blockquote>
    <p>Cannot access java.lang.AbstractStringBuilder",</p>
  </blockquote>
  
  <p>A simple simulation as bellow:</p>
  
  <p>1 - Create an new project with an empty Activity.</p>
  
  <p>2 - Add a Java library module.</p>
  
  <p>3 - library code as bellow:</p>
  
  <pre><code>public class MyClass {
  
      public void add1(StringBuilder sb){
          sb.append("a");
      }
  
      public void add2(StringBuffer sb){
          sb.append("b");
      }
  }
  </code></pre>
  
  <p>4 - activity code as bellow:</p>
  
  <pre><code>MyClass mc=new MyClass();
  StringBuilder sb1=new StringBuilder();
  mc.add1(sb1); // warning: cannot access java.lang.AbstractStringBuilder android
  Log.d("SB1",sb1.toString());
  
  StringBuffer sb2=new StringBuffer();
  mc.add2(sb2); // warning: cannot access java.lang.AbstractStringBuilder android
  Log.d("SB2",sb2.toString());
  </code></pre>
  
  <p>Android is not a client/server type program, I think it should not be an issue of JRE version problem?</p>
  
  <p>I have run "Inspect Code" but didn't find any further information. Any ideas?</p>