Variables and Types

What a Java variable holds and how its type is chosen. The idea that a variable is a box survives about ten minutes of real Java, because half of Java's variables hold an address instead of a value, and that difference decides what assignment does. It covers primitive and reference variables, what copying a variable copies, the eight primitive types, the right type for money, why the compiler refuses some assignments, and why 0.1 + 0.2 is not 0.3. It leaves out fixed-point arithmetic and the wider BigDecimal API.