Derived Data Types-Collections

ArrayList

inta[]=new int a[5];

Limitation of normal array

• Contain same data type of element
• Array size is fixed

Operations On Array List:

1.How to declare array list

2.How to add elements/values to array list

3.Find size of array list

4.remove the element/values from array list

5.insert a new value into array list

6.Read values from array list

1.How to declare array list

ArrayList list=new ArrayList();

ArrayList <String> list=new ArrayList<Strings>();

ArrayList <Integer> list=new ArrayList<Integer>();

2.How to add elements/values to array list

  list.add("John");

  list.add("Smith");

3.Size of array list

 list.size();

4.Remove the element/values from array list

  list.remove(Index);

5.Insert a new value into array list

list.add(index,value)

6.Read values from array list

for(Object s:list) // Object type variable can hold any type of values

{

System.out.printlin(s);

}

HashMap

 

1. How to declare Hashmap
2. Remove elements from Hashmap
3. Read pairs from Hashmap

Declaration:

HashMap <Integer,String> hm=new HashMap<Integer,String>();

Adding pairs into hashmap:

hm.put(101,"John");

hm.put(102,"Scott");

hm.put(103,"David");

hm.put(104,"Smith");

hm.put(105,"Kim");

Print pairs from hasmap:

System.out.println(hm);

Remove a pair from hashmap:

hm.remove(103);

System.out.println("After removing a pair: "+hm)

Reading pairs using for loop:

for(Map.Entry m:hm.entrySet())

{

System.out.println(m.getkey()+" "+m.getValue());

}

JDBC

Java Database Connectivity

Pre-requisite

1.Download database driver(.jar file)

2.Add driver jar to your project

Steps to write JDBC program

1.Create a connection

2.Create a query/statement

3.Execute statement/query

4.close connection

Create a connection:

Connection con=DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521/pdborcl","hr","hr")

Create a query/Statement:

Statement stmt=con.createStatement();

String s="insert into student values(101,'Scott')";

Execute statement query:

stmt.executeQuery(s);

Close connection

con.close();

For select query we need to loop the data from database

String s="select employee_id,first_name,last_name from employees"

ResultSet rs=stmt.executeQuery(s);

while(rs.next())

{

int eid=rs.getInt("EMPLOYEE_ID");

String fname=rs.getString("FIRST_NAME");

String lname=rs.getString("LAST_NAME")

}