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【2014-11-23】《The Hardware/Software Interface》– Section 11
- Data in Java
- Java has pointers – they are called ‘referenes’
- Null is typically represented as 0
- Characters and strings
- Two-byte Unicode instead of ASCII
- Represents most of the world’s alphabets
- String not bounded by a ‘\0’(null character)
- Bounded by hidden length field at beginning of string
- Two-byte Unicode instead of ASCII
- Arrays
- Every element initialized to 0
- Bounds specified in hidden fields at start of array(int – 4 bytes)
- array.length return value of this field
- Every access trigger a bounds-check
- code is added to ensure the index is within bounds
- Exception if out-of-bounds
- Data structures (Object) in Java
- Objects can only include primitive data types
- include complex data types(arrays, other objects, ec.) using references
- Objects can only include primitive data types
- Pointers/References
- Pointers in C can point to any memory address
- References in Java can only point to an object
- And only to its first element – not to the middle of it
- In Java, all variables are reference to objects
- use r.a notation
- Casting in C
- we can cast any pointer into any other pointer
- Casting in Java
- can only cast compatible object references
- Java Methods
- Methods in Java are just functions but with an extra argument: a reference to the object whose method is being called
- Vitual machine and runtime environment
【2014-11-23】《The Hardware/Software Interface》– Section 11
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