Performance Tip: Avoid using String + inside a StringBuilder.append()

Overview

It can make sense to use String + or a StringBuilder however using them in combination is both inefficient and confusing. IMHO make the decision to use one or the other.

From VMId.toString()
result.append((x < 0x10 ? "0" : "") +
          Integer.toString(x, 16));
Here a '0' is optionally added to the start of a number. This could be written as 
result.append((x < 0x10 ? "0" : ""));
result.append(Integer.toString(x, 16));
However using an if statement is likely to be clearer if not at least faster 
if (x < 0x10) result.append('0');
result.append(Integer.toString(x, 16));

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