Java learning Chapter 1 set and ing

Java Learning set and ing in the Life series of programs

1. Collection framework

Three main contents: set list Map

Link Structure:

2. Collection Interface

Set and list parent interfaces, specifically defining some common methods

3. Set and list interfaces: The two interfaces have different extensions for the parent Interface collection.

Set is a set and cannot contain the same elements.

List is a list with the same elements.

4. arraylist: variable-length Array

Sample Code:

Import java. util. date;

Import java. util. arraylist;

Public class testarraylist {

Public static void main (string [] ARGs ){

Arraylist H = new arraylist ();

H. Add ("1st ");

H. Add ("2nd ");

H. Add (New INTEGER (3 ));

H. Add (New Double (4.0 ));

H. Add ("2nd"); // duplicate element, add

H. Add (New INTEGER (3); // duplicate element, add

System. Out. println (h );

System. Out. println ("size =" + H. Size ());

System. Out. println ("----- replace specified Element -----");

H. Set (3, "replace ");

System. Out. println ("----- for loop traversal -----");

For (INT I = 0; I <H. Size (); I ++ ){

System. Out. println (H. Get (I ));

}

System. Out. println ("----- use specific elements -----");

Integer it = (integer) H. Get (2 );

System. Out. println (it. intvalue ());

System. Out. println ("----- insert element -----");

H. Add (3, new date ());

System. Out. println ("----- convert to array -----");

Object [] OS = H. toarray ();

For (Object O: OS ){

System. Out. println (O );

}

}

}

Test results:

5. Vector: note the difference between it and arraylist.

Sample Code:

Import java. util. date;

Import java. util. vector;

Public class testvector {

Public static void main (string [] ARGs ){

Vector v = new vector ();

V. Add ("1st ");

V. Add ("2nd ");

V. Add (New INTEGER (3 ));

V. Add (New Double (4.0 ));

V. Add ("2nd"); // duplicate element, add

V. Add (New INTEGER (3); // duplicate element, add

System. Out. println (v );

System. Out. println ("size =" + v. Size ());

System. Out. println ("----- replace specified Element -----");

V. Set (3, "replace ");

System. Out. println ("----- for loop traversal -----");

For (INT I = 0; I <v. Size (); I ++ ){

System. Out. println (V. Get (I ));

}

System. Out. println ("----- use specific elements -----");

Integer it = (integer) v. Get (2 );

System. Out. println (it. intvalue ());

System. Out. println ("----- insert element -----");

V. Add (3, new date ());

System. Out. println ("----- convert to array -----");

Object [] OS = V. toarray ();

For (Object O: OS ){

System. Out. println (O );

}

}

}

Test results:

6. STACK: a very important data structure that inherits the Vector class.

Sample Code:

Import java. util. date;

Import java. util. Stack;

Public class teststack {

Public static void main (string [] ARGs ){

Stack S = new stack ();

S. Push ("hello ");

S. Push (new date ());

S. Push (400); // automatic encapsulation, equivalent to S. Push (New INTEGER (400 ));

S. Push (1, 3.14 );

System. Out. println ("before the stack: size =" + S. Size ());

System. Out. println (S. Pop ());

System. Out. println ("post-Stack: size =" + S. Size ());

System. Out. println (S. Peek ());

System. Out. println ("after the peek operation: size =" + S. Size ());

While (! S. isempty ())

System. Out. println (S. Pop ());

}

}

Test results:

7. iterator interface: iterator, which is very important. It provides a unified Traversal method for classes that implement the list interface.

Sample Code:

Import java. util. date;

Import java. util. arraylist;

Import java. util. vector;

Import java. util. iterator;

Public class testiterator {

Public static void main (string [] ARGs ){

Arraylist A = new arraylist ();

A. Add ("China ");

A. Add ("USA ");

A. Add ("Korea ");

Iterator it = A. iterator ();

While (it. hasnext ()){

String Country = (string) it. Next ();

System. Out. println (country );

}

Vector v = new vector ();

V. addelement (new date ());

V. addelement (new date (200008755554l ));

It = V. iterator ();

While (it. hasnext ()){

Date time = (date) it. Next ();

System. Out. println (time );

}

}

}

Test results:

8. treeset: Set of sorting functions. The default value is the lexicographical order.

Hashset

Sample Code:

Import java. util. treeset;

Import java. util. iterator;

Public class testtreeset {

Public static void main (string [] ARGs ){

Treeset Ts = new treeset ();

TS. Add ("orange ");

TS. Add ("banana ");

TS. Add ("apple ");

TS. Add ("grape ");

Iterator it = ts. iterator ();

While (it. hasnext ()){

String fruit = (string) it. Next ();

System. Out. println (fruit );

}

}

}

Test results:

Sample Code:

Import java. util. date;

Import java. util. hashset;

Import java. util. iterator;

Public class testhashset {

Public static void main (string [] ARGs ){

Hashset H = new hashset ();

H. Add ("1st ");

H. Add ("2nd ");

H. Add (New INTEGER (3 ));

H. Add (New Double (4.0 ));

H. Add ("2nd"); // duplicate element, not added

H. Add (New INTEGER (3); // duplicate element, not added

H. Add (new date ());

System. Out. println ("START: size =" + H. Size ());

Iterator it = H. iterator ();

While (it. hasnext ()){

Object o = it. Next ();

System. Out. println (O );

}

H. Remove ("2nd ");

System. Out. println ("after removing an element: size =" + H. Size ());

System. Out. println (h );

}

}

Test results:

9. Comparable interface: You can customize the comparison logic by rewriting the compareto method.

Sample Code:

-----------------------------------> Person. Java

Public class person implements java. Lang. Comparable {

Private Final int ID;

Private string name;

Private int age;

Public Person (int id, string name, int age ){

This. ID = ID;

This. Name = Name;

This. Age = age;

}

Public int GETID (){

Return ID;

}

Public void setname (string name ){

This. Name = Name;

}

Public String getname (){

Return name;

}

Public void setage (INT age ){

This. Age = age;

}

Public int getage (){

Return age;

}

Public String tostring (){

Return "ID:" + ID + "\ tname:" + name + "\ Tage:" + age;

}

@ Override

Public int compareto (Object O ){

Person P = (person) O;

Return this. ID-P. ID;

}

@ Override

Public Boolean equals (Object O ){

Boolean flag = false;

If (O instanceof person ){

If (this. ID = (person) O). Id)

Flag = true;

}

Return false;

}

}

----------------------------------------> Test class

Import java. util. treeset;

Import java. util. iterator;

Public class testcomparable {

Public static void main (string [] ARGs ){

Treeset Ts = new treeset ();

TS. Add (new person (1003, "Zhang San", 15 ));

TS. Add (new person (1008, "Li Si", 25 ));

TS. Add (new person (1015, "Wang Wu", 73 ));

TS. Add (new person (1001, "Zhao Liu", 49 ));

Iterator it = ts. iterator ();

While (it. hasnext ()){

Person Employee = (person) it. Next ();

System. Out. println (employee );

}

}

}

10. map interface: save data as key-value pairs

11. hashmap: ing set structure based on hash table

-----------------> Person. Java

Public class person implements java. Lang. Comparable {

Private Final int ID;

Private string name;

Private int age;

Public Person (int id, string name, int age ){

This. ID = ID;

This. Name = Name;

This. Age = age;

}

Public int GETID (){

Return ID;

}

Public void setname (string name ){

This. Name = Name;

}

Public String getname (){

Return name;

}

Public void setage (INT age ){

This. Age = age;

}

Public int getage (){

Return age;

}

Public String tostring (){

Return "ID:" + ID + "\ tname:" + name + "\ Tage:" + age;

}

@ Override

Public int compareto (Object O ){

Person P = (person) O;

Return this. ID-P. ID;

}

@ Override

Public Boolean equals (Object O ){

Boolean flag = false;

If (O instanceof person ){

If (this. ID = (person) O). Id)

Flag = true;

}

Return false;

}

}

-------------------------------------> Test class

Import java. util. Set;

Import java. util. hashmap;

Import java. util. collection;

Import java. util. iterator;

Public class testhashmap {

Public static void main (string [] ARGs ){

Hashmap Hm = new hashmap ();

Hm. Put (New INTEGER (1003), new person (1003, "James", 15 ));

Hm. Put (New INTEGER (1008), new person (1008, "Li Si", 25 ));

Hm. Put (1015, new person (1015, "Wang Wu", 73); // automatically encapsulate

Hm. Put (1001, new person (1001, "Zhao Liu", 49 ));

System. Out. println ("---- retrieving a single element ----");

Person P = (person) Hm. Get (1008 );

System. Out. println (P );

System. Out. println ("---- traverse all \" keys \ "(element name )----");

Set names = hm. keyset ();

For (Object O: names ){

System. Out. println (O );

}

System. Out. println ("---- traverse all \" value \ "(element value )----");

Collection values = hm. Values ();

For (Object O: values ){

System. Out. println (O );

}

}

}

Hashtable and hashmap are basically the same, but there are also some differences

Thread security is generally used in multi-threaded environments.

12. arrays class: array class. There are many static methods available for direct calls by arrays.

Sample Code:

Import java. util. List;

Import java. util. arrays;

Public class testarrays {

Public static void main (string [] ARGs ){

Integer [] A = {3, 25, 12, 79, 48 };

System. Out. println ();

System. Out. println (arrays. tostring ());

Arrays. Sort ();

System. Out. println (arrays. tostring ());

Int idx = arrays. binarysearch (A, 25 );

System. Out. println (idx );

List list = arrays. aslist (3, 4, 5 );

System. Out. println (list );

List. Set (2,66 );

System. Out. println (arrays. tostring ());

}

}

Test results:

13. Collections class: it defines many methods to operate on a set.

Sample Code:

Import java. util. vector;

Import java. util. arraylist;

Import java. util. collections;

Import java. util. enumeration;

Public class testcollections {

Public static void main (string [] ARGs ){

Arraylist alist = new arraylist ();

Alist. Add (75 );

Alist. Add (38 );

Alist. Add (21 );

Alist. Add (4 );

Alist. Add (12 );

System. Out. println ("original list:" + alist );

Collections. Sort (alist );

System. Out. println ("sorted:" + alist );

Collections. Reverse (alist );

System. Out. println ("back-to-order:" + alist );

Collections. Shuffle (alist );

System. Out. println ("after mixing:" + alist );

Collections. Rotate (alist, 2 );

System. Out. println ("after shift:" + alist );

Arraylist blist = new arraylist ();

Blist. Add (55 );

Blist. Add (66 );

System. Out. println ("new list:" + blist );

Collections. Copy (alist, blist );

System. Out. println ("after copying:" + alist );

System. Out. println ("Number of times element 66 is displayed in the list:" + collections. Frequency (alist, 66 ));

System. Out. println ("Maximum number of elements in the list:" + collections. Max (alist ));

System. Out. println ("minimum value of the element in the list:" + collections. Min (alist ));

Enumeration en = createdemoenumeration ();

Arraylist clist = collections. List (en );

System. Out. println ("enumeration-> arraylist:" + alist );

}

Public static enumeration createdemoenumeration (){

Vector v = new vector ();

V. Add ("Tom ");

V. Add ("Billy ");

V. Add ("Jenny ");

Return v. Elements ();

}

}

Test results: