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:
Datatypevariablename;
CONSTANT: It is a name given to a memory location, which
can hold a value that can’t be changed in future.
Syntax: final Datatypeconstantname=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)
datatypearrayname[]= new
datatype[size];
Multi
Dimensionalarray : to store more
no of multiple values very easily we should use
this array
Syntax:
datatype[][] arrayname= new datatype[size][size]; (OR)
datatypearrayname[][]= 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;
publicclass array {
publicstaticvoid 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:
ArrayListclass ,Hashtable class are predefined class of collection API in java.
ArrayListclass : 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;
importjava.util.ArrayList;
publicclassarraylistclass {
publicstaticvoid 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=newArrayList<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());
publicclass array {
publicstaticvoid main(String[] args) {
ArrayList<String>
a=newArrayList<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………………………………………………..
packagesetlist;
importjava.util.ArrayList;
importjava.util.List;
publicclass list {
publicstaticvoid main(String[] args) {
ArrayList<String>
a=newArrayList<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=newHashSet<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=newHashSet<>();
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);
Hashtableclass :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);
publicclasshashtable {
publicstaticvoid 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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