Java basic programming structure (5)

(9) large values
This stuff is generally not very commonly used, so let's simply put it here.
First, it must be used more than 32 bits. It is two useful classes included in the Java. Math package.
Biginteger and bigdecimal

Note that they cannot use-+/* = and need to use add (); subtract ();
Multiply ();
Divide ()
MoD ();
Compareto ();
Valueof ();

(10) array

Initialization
Int A [] = new int [20];
Int C []; // declare array variable
C = new int [12]; // create Array
For (INT I = 0; I <A. length; I ++)
A [I] = I;
For (int I:)
System. Out. println (I );

You can declare an array variable either
Int [] A; or
Int A [];

1. "for each" Loop

For (INT element:)
System. Out. println (element );
The above is equivalent to the following
For (INT I = 0; I <A. length; I ++)
System. Out. println (A [I]);

2. array initializes and anonymous Arrays
Int smallints [] = {1, 2, 3 };
String [] cardinals = {"one", "two", "three "};
String [] ordinals = {"first", "second", "third "};

Anonymous Array
New int [] {12, 23, 23, 23}
It seems useless.

3. Copy an array
System. arraycopy (from, fromindex, to, toindex, count );
Example:
Int [] smallprimes = {2, 3, 5, 7, 11, 13 };
Int [] luckynumbers = {1001,100 2, 1003,100 4, 1005,100 6, 1007 };
System. arraycopy (smallprimes, 2, luckynumbers, 3, 4 );
For (INT I = 0; I <luckynumbers. length; I ++)
System. Out. println (I + ":" + luckynumbers [I]);

Result:
0: 1001
1:1002
2: 1003
3:5
4: 7
5: 11
6:13

4. Command Line Parameters
Public static void main (string [] ARGs ){

For (INT I = 0; I <args. length; I ++)
System. Out. println (ARGs [I]);

}

5. array sorting
(Math. Random () * n; // generate a random number ranging from 0 to n-1.
Random () generates 0-1 (not including 1 floating point numbers)

Arrays. Sort (result); // sort

6. Multi-dimensional array

Balance = new double [nyears] [nrates];
// You cannot use the array until you new and initialize it

Int [] [] magicsquare =
{
{16, 3, 2, 13, 23 },
{5, 10, 11, 8, 3 },
{9, 6, 7, 12, 67 },
{4, 15, 14, 1, 44}
}; // Note: no "new"

7. Irregular Array
The length of each line is also different.
Example of initialization:
Int [] [] Odds = new int [NMA + 1] [];
For (INT I = 0; I <= NMA; n ++)
{
Odds [N] = new int [n + 1];
}
For (INT n = 0; n <odds. Length (); N ++)
{
For (int K = 0; k <odds [N]. Length (); k ++)
{
Odds [N] [k] = lotteryodds;
}
}

8. Vector
Similar to an array, but the size does not need to be declared
Can contain different object types

Initialization:
Vector VEC = new vector ();

Some useful methods:
Isempty ()
Indexof (Object Arg)
Contains (Object Arg)

Example:
Vector VEC = new vector ();
VEC. addelement ("one ");
VEC. addelement ("two ");
VEC. addelement ("three ");
Enumeration E = Vec. Elements ();
While (E. hasmoreelements ()){
System. Out. println ("element =" + E. nextelement ());
}
Result:
Element = one
Element = two
Element = three

9. Collection
Constructor ()
Creates a collection with no elements
Size ()
Number of elements in the collection
Boolean add ()
Add a new pointer/element at the end of the collection
Returns true is the collection is modified.
Iterator ()
Returns an iterator object
Hasnext ()-returns true if more elements
Next ()-returns the next element
Remove ()-removes element returned by previous next () call.

Example
It = strings. iterator ();
While (it. hasnext ()){
It. Next (); // get pointer to ELEM
It. Remove (); // remove the above ELEM
}

System. Out. println ("Size:" + strings. Size ());