• A lot like C/C++
• A lot NOT like C/C++

Character set

• Unicode character set (16 bits wide)
• locale -- accomodates customization for culture, language, country
• Identifiers are also wrttten in Unicode

Primitive Types and Their Literals

• boolean
  • Literals: true, false
  • NOT compatible with integer types
    • Eliminates good ol' 'assignment instead of equality' mistake in C/C++
    • On the other hand, prevents certain 'standard' C idioms
• integers - byte (8), short (16), int (32), long (64)
  • Literals: 123 (decimal), 0475 (octal), 0x7D5C hexadecimal
  • Cross-platform executables requires standardized integer lengths
  • Executing on the JVM (virtual machine) makes this a moot point
  • No unsigned types
  • Default integer literal type is int; L can be used as a suffix to force long
• character - char
  • Literals: 'a', '\u00E6', '\n'
• floating point - float (64), double (128)
  • Literals: 0.0, .53, 1e99
  • Default floating literal type is double; F can be used as a suffix to force float

String Literals

• String class possesses a literal, even though not primitive type
• Sequence of characters in doublke quotes: "Hello", "\u5469 \u5561"

Operators and Expressions

• Similar to C/C++
• Numerics include integer and floating point
• Inreger operators appply to char as well
• As in C, integer arithmetic wraps around (rather than under/over-flowing)
• String concatenation
  • "Dear " + name + ": "
  • Shouldn't really be there (no operator overloading in Java)
  • Ubiquitous and useful, so was add
  • If one of the operands is non-string, it is converted to String (more on how later)

Variables and Types

• Declaration syntax similar to C/C++
• A type specifies the legal values a variable (of that type) may contain
• primitive and reference types
  • variable of reference type hold a reference to an object
  • (shhh-- if you promise not to tell anyone, I'll let you think of a reference as a pointer)
• Default initial values
  • Basically the value when stuffed with 0's
  • Doesn't happen with locals

Type Compatibility and Conversion

• Types are compatible if each can appear in contexts that the other may appear
• Conversion involves transforming a value of one type to a value of another type
• In a widening conversion, the value is converted to one of a larger range (int -> long, int->double)
  • Safe, so is done implicitly when required
• In a narrowing conversion, the value is converted to one of a smaller range (double -> float, float->long)
  • Unsafe (why?), so explixit cast is required

Reference Types

• class, interface, array type
• reference variable is a variable of reference type
  • contains a reference to object (of that type)
  • may also contain null -- indication no object is being referenced
• References are NOT pointers (so forget what I said before!)
  • In C/C++, pointers are recognized for what they are ((32-bit) integers voewed as addresses)
    • Pointers can be cast to other pointer types
    • Pointers can be manipulated via pointer arithmetic
    • Pointers can be used to work with dynamically-allocated memory
      • heap-allocation
      • allocation and deallocation under programmer control
  • None of this is allowed, provided for, or required by Java
    • Java's heap is garbage-collected

Object Creation

• Declaration
  • Specifies type of (reference) variable
  • Allocates space for the reference
  • Does NOT allocate space for an object
• new operatro creates objects
• Equality
  • == indicates equality of references
  • equals method is used for (semantic) equality of objects
    • class designer's responsibility to code a proper equals method

Arrays

• Improvement over C/C++ declaration syntax
• Creating
• 'Resizing'