java study notes 2

collection container interface

set cannot be repeated unordered
list can be repeated ordered
 
hashMap ->map find objects through objects

iterator iterates over a container

link

ArraryList Thread unsafe High efficiency Low-level implementation is array Query, block join and delete slow
LinkList Thread unsafe High efficiency Low-level implementation is linked list Slow query Add block
Vector Thread safe Low efficiency

System.Arrarycopy();
Array copy

Map key (key)-value (value) segment health does not repeat
Map.put (key, value) one-to-one put similar correlation

hashMap() thread unsafe high efficiency
hashTable() thread safe high efficiency

The bottom layer of set is Map, the
default hashcode is calculated according to the address

The bottom layer of hasdset is hasdmap and the object of hashset is used as the key of hashmap

remove according to

set hash

After adding generics to the container, only one type of object can be added
List<Student> list = new ArraryList<Student>();

javabean entity class properties are similar to set and get methods
map

Iterator interface (iterator) container variable

First get the iterator then loop

Student<T1,T2> 
Student<String,Integer> cannot be static Basic data type
T type
kv key value

In a generic interface interface, generic letters can be used in methods but not in constants

Generic method can only get information cannot be modified
  public static <T> void test(T a) {
      System.out.println();
 }
Generic type Automatically check polymorphic type

The parent class is a generic class
public abstract class Father<T> {
}
Subclass (1) Class class child1 extends Father<String> {
}
      (2) When using a generic class, make sure the number is the same as the number of letters of the parent class
              type child2<T> extends Father(T) {
}
       (3) The subclass is a generic class, and the parent class does not specify a type. Generic
              erasure class child3<T1> extends Father{
}
        (4) Subclass erasures parent class erasure except
             class child4 extends Father {
}

In the parent class follow the parent classIn the subclass follow the subclass
Override follow the parent class

Paradigm without polymorphism Can't be used on
classes ?
extends <= upper limit
super >= lower limit

generic nesting

No generic array
can be declared available?

jdk1.7 can A<String> x = new A<>();

Use generics Do not specify a type Erase the default Object 
but customize the Object by yourself Not erasing but comparing with Object when using

Enhanced for must implement iterator and enhanced for is iterator
Java.lang.Iterable interface

The built-in sorting system implements the Comparable interface and overrides the
CompareTo() method

Our custom sorting needs to implement the Compare method of the Comparator interface

TreeSet

The data cannot be modified when used, otherwise the sorting may be disrupted
because it is sorted when placed

Use final modifier

hashMap hashTable difference
hashtable thread safety relatively low synchronization efficiency
hashmap thread safety asynchronous high efficiency
parent class hashtable Dictionry hashMap AbstractMap
null hashtable key and value cannot be null
     hashMap health at most one null value can be multiple Null

Properties   Read and
write resource configuration files
Values ​​and keys can only be strings

The suffix is ​​properties
byte stream
character
stream.xml

The WeakhashMap key is a weak reference gc immediately reclaims
the IdentityMap key and compares the address Note that the constant pool object
EnumMap enumerates the Map key is the enumeration value

Collections manage synchronization, that is, the container becomes a thread-safe container
SynchronizationXXX();
Collections, synchronizationList();

Collection read-only set
empty

https://code.google.com/p/guava-libraries/

ByteArrayOutputStream needs to save the data in the node stream to byteArrayOutputStream and then unify the
bos, toByteArray() method and output it to the byte array

Reference Type Data + Type
Serialization Input Stream ObjectInputStream
Deserialization Output Stream ObjectOutputStream

Serialization and deserialization are in the same order
Not all objects can be serialized must implement the java.io.Serializable interface

Not all properties need to be serialized Do not want a property to be serialized
private transient String name;

public static void close(Closeanle ... io)
variable parameters (number) can only be placed at the end

1.7 New features try --- with --- resource
automatically closes the same after compilation

printstream  = system.out;

redirect

RandAccessFile random read can be used for file splitting
RandAccessFile(src."r") read only

sequenceInputStream merges two streams
uses Vector to store enumeration streams