Here is some more sample code demonstrating matrix equivalence based on the order of operations on that matrix

TestMatrix.java

public class TestMatrix 
{
   public static void test(SomeActivity a)
   {
      test1(a);
      test2(a);
      test3(a);
   }
   public static void test1(SomeActivity a)
   {
      Matrix m1 = new Matrix();
      m1.setScale(2, 2);
      m1.preScale(2, 2);
      m1.postScale(2, 2);
      
      Matrix m2 = new Matrix();
      m2.postScale(2, 2);
      m2.postScale(2, 2);
      m2.postScale(2, 2);

      assertL("test1",a,m1,m2,"m1 and m2 will be same");
   }
   
   public static void test2(SomeActivity a)
   {
      Matrix m1 = new Matrix();
      m1.setScale(2, 2);
      m1.preTranslate(-2, -2);
      m1.postTranslate(2, 2);
      
      Matrix m2 = new Matrix();
      m2.postTranslate(-2, -2);
      m2.postScale(2, 2);
      m2.postTranslate(2, 2);
      
      assertL("test2",a,m1,m2,"m1 and m2 will be the same");
   }
   
   public static void test3(SomeActivity a)
   {
      Matrix m1 = new Matrix();
      m1.setScale(2, 2);
      m1.preTranslate(-2, -2);
      m1.postTranslate(2, 2);
      
      Matrix m2 = new Matrix();
      m2.preTranslate(-2, -2);
      m2.postTranslate(2, 2);
      m2.setScale(2, 2);

      assertL("test4",a,m1,m2,"m1 and m2 will not be the same");

      Matrix m3 = new Matrix();
      m3.setScale(2, 2);
      assertL("test3",a,m2,m3,"m2 and m3 will be the same");
   }
   
   private static void assertL(String testName
         , SomeActivity a
         , Matrix m1
         , Matrix m2
         , String assertText)
   {
      if (m1.equals(m2))
      {
         a.appendText("\n" + testName + ": m1 is same as m2");
      }
      else
      {
         a.appendText("\n" + testName + ": m1 is NOT same as m2");
      }
   }
}