VARIABLE: It is a name given to a memory location, which
can hold a value and that can be changed any number of times in future if
required.
Adv: Reusability
& easy to maintain (future updations are easy) .
NOTE: always use meaningful names.
Syntax:
Datatype variablename;
CONSTANT: It is a name given to a memory location, which
can hold a value that can’t be changed in future.
Syntax: final Datatype constantname=value;
if…. else
CONDITIONAL
STATEMENTS :( decision making statements)
In java we
have two types of conditional statements.
If …else
Switch… case
IF--- ELSE:
whenever we want to execute one block of statements
among two blocks then we can use If..Else.
Syntax: if(condition)
{ block of stmts1 } else { block of stmts2 }
Note :
condition is true then block of stmts1 will be executed
Switch…case: Whenever we want to execute a particular block of
statements among many blocks then we will choose switch case statement.
Syntax: switch(choice) {
case “c1”:
block1
break;
case “c2”:
block 2
break;
-----------
Default: ------ // not mandatory
}
LOOPING
STATEMENTS: Looping
statements are used for executing a certain block of statements repeatedly and
continuously for some number of times.
in java we
have 3 types of looping statements
for loop
while loop
do…while loop
for
loop: whenever we
clearly know how many no of times the block should be repeated then use for loop.
syntax :
for(initiation ;condition ;improvement)
{
----------------
block of stmts
}
While
loop: It is used
for executing a block of statements repeatedly as long as the condition is
being satisfied.
Syntax: while(
condition)
{ ------- block of stmts
}
do----
while loop: It is used
for executing a block of statements repeatedly as long as the condition is
being satisfied, but first time execution will be done without checking the
condition.
Syntax: do {
-------------block of stmts
} while(condition)
;
ARRAYS: Array is a
special type of variable which can hold multiple values.
in java we
have the following types of arrays
single
Dimensional array
multi
Dimensional array
For storing
and retrieving values to and from array we will use index. Index starts with 0
and continues like 1.2.3……
Single
Dimensional array
Syntax:
datatype[] arrayname= new datatype[size];
(OR)
datatype arrayname[]= new
datatype[size];
Multi
Dimensional array : to store more
no of multiple values very easily we should use
this array
Syntax:
datatype[][] arrayname= new datatype[size][size]; (OR)
datatype arrayname[][]= new
datatype[size][size];
Object
array: it is used for storing multiple
values of different datatypes
Syntax:
Object[] arrayname= new Object[size];
(OR)
Object arrayname[]= new
Object[size];
object array:
package pack1;
public class array {
public static void main(String[] args) {
Object a[]=new Object[6];
a[0]="akhil";
a[1]="sindu";
a[4]=3.14;
a[2]=100;
a[3]="haritha";
a[5]='a';
System.out.println(a[4]); }
}
ArrayList class
Hashtable class
Note: ArrayList
class ,Hashtable class are predefined class of collection API in java.
ArrayList class : it is used
for simulating dynamically growing array.
Syntax: ArrayList<datatype> arrayname= new
ArrayList<datatype>();
For retrieving values from this we will use index.
Index starts with 0 and continues like 1.2.3……
To add data to this array we need to use the below
syntax
Syntax: arrayname.add(data);
package array;
import java.util.ArrayList;
public class arraylistclass {
public static void main(String[] args) {
a.add("akhil");
a.add("swapna");
a.add("sindhu");
a.add("haritha");
a.add("akhil");
a.add("swapna");
a.add("sindhu");
a.add("haritha");
System.out.println(a.get(2));
}
}
ArrayList <String> a=new ArrayList <String>();
a.add("akhil");
a.add("swapna");
a.add("sindhu");
a.add("haritha");
a.add("akhil");
a.add("swapna");
a.add("sindhu");
a.add("haritha");
System.out.println(a.get(2));
System.out.println(a.size());
public class array {
public static void main(String[] args) {
ArrayList
<String> a=new ArrayList <String>();
a.add("akhil");
a.add("swapna");
a.add("sindhu");
a.add("haritha");
a.add("akhil");
a.add("swapna");
a.add("sindhu");
a.add("haritha");
System.out.println(a.size());
System.out.println(a.get(0));
System.out.println(a.get(1));
System.out.println(a.get(2));
System.out.println(a.get(3));
System.out.println(a.get(4));
System.out.println(a.get(5));
System.out.println(a.get(6));
System.out.println(a.get(7));
}
}
For………………………………………………..
package setlist;
import java.util.ArrayList;
import java.util.List;
public class list {
public static void main(String[] args) {
ArrayList
<String> a=new ArrayList <String>();
a.add("akhil");
a.add("swapna");
a.add("sindhu");
a.add("haritha");
a.add("akhil");
a.add("swapna");
a.add("sindhu");
a.add("haritha");
a.add("akhil");
a.add("swapna");
a.add("sindhu");
a.add("haritha");
a.add("akhil");
a.add("swapna");
a.add("sindhu");
a.add("haritha");
a.add("akhil");
a.add("swapna");
a.add("sindhu");
a.add("haritha");
a.add("akhil");
a.add("swapna");
a.add("sindhu");
a.add("haritha");
a.add("akhil");
a.add("swapna");
a.add("sindhu");
a.add("haritha");
a.add("akhil");
a.add("swapna");
a.add("sindhu");
a.add("haritha");
a.add("akhil");
a.add("swapna");
a.add("sindhu");
a.add("haritha");
a.add("akhil");
a.add("swapna");
a.add("sindhu");
a.add("haritha");
System.out.println(a.size());
for(int
i=0;i<40;i++)
{
System.out.println(a.get(i));
}
}
SET: Set is an
interface belongs to the collection API which is implemented by a class
HashSet: It is similar
to ArrayList it will be dynamically growing but will hold only unique values
(even though you add duplicate values but it will take only one value in to the
set).
Syntax: Set<datatype>
setname=new
HashSet<datatype>();
To
add values in to a set we have the same add() method which is also available in
the ArrayList.
Syntax: setname.add(data);
Note: here above
data‘s data type must be set declaration’s data type
To retrieve
values form a set here we don’t have get() method as like in ArrayList, so for
this concept we have an interface Iterator in java.
Syntax: Iterator<datatype>
iteratorreference=setname.iterator();
Note: here
Iterator’s data type & setname’s data type must be same.
Iterator: Iterator is
an interface belongs to the collection API which is used to handle sets, list
and so on. Simply Iterator reference acts like a pointer.
Useful methods in Iterator interface for doing
testing as follows
hasNext(): it checks
whether Iterator reference has next element
available or not ,returns true if it has next element otherwise returns
false.
next(): it gets
element’s data from the location which is pointed by Iterator reference.
Set<String>
l=new
HashSet<>();
l.add("a1");
l.add("a2");
l.add("a2");
l.add("a3");
l.add("a4");
l.add("a");
l.add("a1");
l.add("a2");
l.add("a2");
l.add("a3");
l.add("a4");
System.out.println(l.size());
Iterator<String>
itr=l.iterator();
for(int i=0;i<l.size();i++)
{
System.out.println(itr.next());
}
l.add("a6");
itr=l.iterator();
System.out.println(l.size());
for(int
i=0;i<l.size();i++)
{
System.out.println(itr.next());
}
l.add("a7");
itr=l.iterator();
System.out.println(l.size());
for(int
i=0;i<l.size();i++)
{
System.out.println(itr.next());
}
l.add("a8");
itr=l.iterator();
System.out.println(l.size());
for(int
i=0;i<l.size();i++)
{
System.out.println(itr.next());
}
}
}
Note: here data is of same data type’s data by the
time of declaration
To access(retrieve) data from this array we need
to use the below syntax
Syntax: arrayname.get(indexno);
Hashtable class : is used for
simulating dynamically growing array.
For storing and retrieving values to and from this
we will use keys instead of Index
Syntax: Hashtable<datatype1, datatype2>
arrayname= new Hashtable<datatype1, datatype2>();
datatype1 is for keys & datatype2 is for
values and datatype1 ,datatype2 are datatype’s class name
To add data to this array we need to use the below
syntax
Syntax: arrayname.put(data, data);
Note: here data is of same data type’s data by the
time of declaration
To access(retrieve) data from this array we need
to use the below syntax
Syntax: arrayname.get(key);
public class hashtable {
public static void main(String[] args) {
a.put("akhil","hyd");
a.put("swapna","hyd2");
a.put("sindhu","tmnd");
a.put("haritha","usa");
a.put("swapna1","hhhhhh");
a.put("sindhu1","kkkkk");
a.put("haritha1","jjjjjj");
System.out.println(a.size());
System.out.println(a.get("haritha"));
System.out.println(a.get("kkkkk"));
}
}
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