Java
classes
- Objects are either of primitive type or reference
type. Object is the base for all reference
types, look for SoftReference and
WeakReference within java.lang.ref. Get
Class for inspection and, within
java.lang.reflect, Modifier,
AnnotatedElement◊
- Among Throwable, Error (unchecked)
and Exception (checked). However, in the latter,
there is RuntimeException (unchecked). To debug,
StackTraceElement and
java.util.logging.
Runtime gives access to the OS environment, and
System to SecurityManager and
Properties.
Type Width Default Examples of constants
bool ≥ 1 false false true
char 16 '\u0000' 'C' '\u0043'
byte 8 0 26 032 0x1a
short 16 0
int 32 0
long 64 0
float 32 0.0f 123.4f
double 64 0.0d 123.4, 1.234e2
For classes
boxing primitive types, use this chart:
boxed unboxed
Boolean bool
Character char
Number Byte byte
Short short
Integer int
Long long
Float float
Double double
Also see
Void.
- For arithmetic: Number and Math.
Number is also extended by BigInteger,
BigDecimal, AtomicInteger and
AtomicLong, see common methods implemented in
all its subtypes.
- For characters and strings: Character,
String, StringBuilder and
StringBuffer. Also, within
java.util.regex: Pattern, Matcher
and PatternSyntaxException.
Example of a
constant string: "ABC\\\"\'\t\f\r\n\u0042xyz".
- Declaration: TYPE[DIM] VARIABLE;
- Allocation: VARIABLE = new TYPE[DIM];
- Literal: {【EXPRESSION【, EXPRESSION】☼】♭}
- Attributes
- Useful:
void arraycopy(Object src, int srcPos,
Object dest, int destPos,
int length)
- Also see Arrays, Comparator◊ and
Comparable◊.
Calendar.
- The
collection framework is based on Collection◊
(and Iterator◊, which replaces
Enumeration◊). Collections holds related
utilities.
- Set◊ includes HashSet, TreeSet
and LinkedHashSet. There is also
SortedSet◊. EnumSet and
CopyOnWriteArraySet are special
implementations.
- List◊ includes ArrayList and
LinkedList (and ListIterator◊). Older
Vector has been amended as well.
CopyOnWriteArrayList is a special
implementation.
- Queue◊ includes LinkedList.
PriorityQueue is a special implementation.
BlockingQueue◊ includes
LinkedBlockingQueue, ArrayBlockingQueue,
PriorityBlockingQueue, DelayQueue and
SynchronousQueue.
- Map◊ includes HashMap, TreeMap
and LinkedHashMap. Older Hashtable (a
kind of Dictionary) has been amended as well.
There is also SortedMap◊ and
NavigableMap◊. EnumMap,
WeakHashMap and IdentityHashMap are
special implementations. ConcurrentMap◊ includes
ConcurrentHashMap, while
ConcurrentNavigableMap◊ includes
ConcurrentSkipListMap.
- Besides the basics, mainly within
java.util.concurrent,
java.util.concurrent.locks and
java.util.concurrent.atomic.
- ProcessBuilder may create Process
objects.
- Runnable◊ includes Thread.
- Lock◊ includes ReentrantLock, which
may create Condition◊.
- Executor◊ (and derived interfaces) may go
through Executors tools. In particular, they may
accept Callable◊ and return Future◊.
- Mainly within java.io, but also within
java.nio.
- Handling File names and FileLock, and
RandomAccessFile.
- For unbuffered input/output: FileInputStream
and FileOutputStream are byte oriented.
FileReader and FileWriter are character
oriented. InputStreamReader and
OutputStreamWriter establishes a bridge between
byte oriented and character oriented.
- For buffered input/output:
BufferedInputStream and
BufferedOutputStream are byte oriented.
BufferedReader and BufferedWriter are
character oriented.
- For binary input/output: DataInputStream and
DataOutputStream for primitive types.
ObjectInputStream and ObjectOutputStream
for serializable types.
- For in-memory input/output:
ByteArrayInputStream and
ByteArrayOutputStream are byte oriented.
CharArrayReader and CharArrayWriter are
character oriented.
- For Formatted input/output: Scanner
and Formatter are related tools.
PrintStream is byte oriented, yet it features a
character stream internally. This is historically the
type of System.{out,err}. PrintWriter is character
oriented. Console may be used if standard
streams are not redirected. System.in is byte oriented and has no
character feature.
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