code: @Override
      public void sawOpcode(int seen) {
  
          try {
              stack.precomputation(this);
  
              if ((seen == Const.INVOKEVIRTUAL) || (seen == Const.INVOKEINTERFACE)) {
                  FQMethod key = new FQMethod(getClassConstantOperand(), getNameConstantOperand(), getSigConstantOperand());
  
                  Object posObject = characterMethods.get(key);
                  if (posObject instanceof Integer) {
                      if (checkSingleParamMethod(((Integer) posObject).intValue()) && !isInlineAppend(key)) {
                          reportBug();
                      }
                  } else if ((posObject instanceof IntPair) && checkDoubleParamMethod((IntPair) posObject)) {
                      reportBug();
                  }
  
              } else if (seen == Const.DUP) {
                  if (stack.getStackDepth() > 0) {
                      OpcodeStack.Item itm = stack.getStackItem(0);
                      String duppedSig = itm.getSignature();
                      if (Values.SIG_JAVA_UTIL_STRINGBUILDER.equals(duppedSig) || Values.SIG_JAVA_UTIL_STRINGBUFFER.equals(duppedSig)) {
                          itm.setUserValue(UCPMUserValue.INLINE);
                      }
                  }
              } else if ((seen == Const.PUTFIELD) || (((seen == Const.PUTSTATIC) || OpcodeUtils.isAStore(seen)) && (stack.getStackDepth() > 0))) {
                  OpcodeStack.Item itm = stack.getStackItem(0);
                  itm.setUserValue(null);
              }
          } finally {
              UCPMUserValue uv = callHasInline(seen);
  
              stack.sawOpcode(this, seen);
              if ((uv == UCPMUserValue.INLINE) && (stack.getStackDepth() > 0)) {
                  OpcodeStack.Item itm = stack.getStackItem(0);
                  itm.setUserValue(uv);
              }
          }
      }
docs: implements the visitor to look for method calls that pass a constant string as a parameter when the string is only one character long, and there is an
  alternate method passing a character.