Collections-
it is nothing but the framework defined in java.
it provides architecture to store & manipulate the group of objects.
Clasess & interfaces-
1) arraylist-
ex-
package collectionsp;
import java.util.ArrayList;
public class ArrayListClass {
public static void main(String[] args) {
int [] i=new int[3];
ArrayList <Integer> al=new ArrayList<Integer>();
al.add(10);
al.add(20);
al.add(30);
System.out.println(al);
ArrayList <String> al1=new ArrayList<String>();
al1.add("Pune");
al1.add("Mumbai");
al1.add("Thane");
System.out.println(al1);
List of method-
add()- add data in the list
set();- set values at gievn index
remove()-
removeAll()-
addAll()-
ex-
package collectionsp;
import java.util.ArrayList;
public class ArrayListClass {
public static void main(String[] args) {
ArrayList <Integer> al=new ArrayList<Integer>();
al.add(10);
al.add(20);
al.add(30);
al.add(40);
System.out.println(al);
ArrayList <Integer> al1=new ArrayList<Integer>();
al1.add(70);
al1.add(80);
al1.add(90);
//al.addAll(al1);
System.out.println(al);
if (!al.containsAll(al1)) {
System.out.println("True");
al.addAll(al1);
} else {
System.out.println("false");
}
System.out.println(al);
package collectionsp;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
public class ArrayListClass {
public static void main(String[] args) {
//From list to arrays
ArrayList <String> al=new ArrayList<String>();
al.add("pune");
al.add("Mumbai");
al.add("Thane");
al.add("Nashik");
System.out.println(al);
String []arrays=new String[al.size()];
al.toArray(arrays);
for (String itr:arrays) {
System.out.println(itr);
package collectionsp;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
public class ArrayListClass {
public static void main(String[] args) {
//From arrays to List conversion
String []arrays= {"Nagpur", "Manmad", "Ahmednagr"};
//From list to arrays
ArrayList <String> al=new ArrayList<String>(Arrays.asList(arrays));
al.add("pune");
al.add("Mumbai");
al.add("Thane");
al.add("Nashik");
System.out.println(al);
}
}
Arraylist are follwing insertion order.
Arraylist allows duplicate values.
ex-
package collectionsp;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.LinkedList;
import java.util.List;
public class ArrayListClass {
public static void main(String[] args) {
//From arrays to List conversion
String []arrays= {"Nagpur", "Manmad", "Ahmednagr"};
//From list to arrays
ArrayList <String> al=new ArrayList<String>(Arrays.asList(arrays));
al.add("pune");
al.add("pune");
al.add("Mumbai");
al.add("Mumbai");
al.add("Thane");
al.add("Nashik");
System.out.println(al);
if (al.contains("Mumbai")) {
al.remove("Mumbai"); }
System.out.println(al);
if (!al.contains("Aurangabad")) {
al.add("Aurangabad");
}
System.out.println(al);
LinkedList<String> ll=new LinkedList<String>();
ll.add("Hi");
ll.add("Bye");
ll.addAll(al);
System.out.println(ll);
}
}
when we want to iterate on the values of cxollection
ex-
package collectionsp;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
public class ArrayListClass {
public static void main(String[] args) {
//From arrays to List conversion
String []arrays= {"Nagpur", "Manmad", "Ahmednagr"};
//From list to arrays
ArrayList <String> al=new ArrayList<String>(Arrays.asList(arrays));
al.add("pune");
al.add("pune");
al.add("Mumbai");
al.add("Mumbai");
al.add("Thane");
al.add("Nashik");
System.out.println(al);
if (al.contains("Mumbai")) {
al.remove("Mumbai"); }
System.out.println(al);
if (!al.contains("Aurangabad")) {
al.add("Aurangabad");
}
System.out.println(al);
LinkedList<String> ll=new LinkedList<String>();
ll.add("Hi");
ll.add("Bye");
ll.addAll(al);
System.out.println(ll);
Iterator<String> itr=ll.iterator();
while(itr.hasNext()) {
String value=itr.next();
System.out.println(value);
}
--------------------------------
When we dont want to maintain insertion order and duplicate value
then we go for Hashset.
ex-
package collectionsp;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
public class ArrayListClass {
public static void main(String[] args) {
//From arrays to List conversion
String []arrays= {"Nagpur", "Manmad", "Ahmednagr"};
//From list to arrays
ArrayList <String> al=new ArrayList<String>(Arrays.asList(arrays));
al.add("pune");
al.add("pune");
al.add("Mumbai");
al.add("Mumbai");
al.add("Thane");
al.add("Nashik");
System.out.println(al);
HashSet<String> hs=new HashSet<String>();
hs.add("Dubai");
hs.add("Bankok");
hs.addAll(al);
System.out.println(hs);
}
Treeset-
No null values accpted
By default is scending order
Duplicate are not allowed
ex-
package collectionsp;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.NavigableSet;
import java.util.TreeSet;
public class ArrayListClass {
public static void main(String[] args) {
//From arrays to List conversion
String []arrays= {"Nagpur", "Manmad", "Ahmednagr"};
//From list to arrays
ArrayList <String> al=new ArrayList<String>(Arrays.asList(arrays));
al.add("Pune");
al.add("Pune");
al.add("Mumbai");
al.add("Mumbai");
al.add("Thane");
al.add("Nashik");
System.out.println(al);
HashSet<String> hs=new HashSet<String>();
hs.add("Dubai");
hs.add("Bankok");
hs.addAll(al);
hs.add(null);
hs.add(null);
System.out.println(hs);
LinkedHashSet<String>lhs=new LinkedHashSet<String>();
lhs.add("Dubai");
lhs.add("Bankok");
lhs.addAll(al);
lhs.add(null);
System.out.println(lhs);
TreeSet<String> tr=new TreeSet<String>();
tr.addAll(al);
System.out.println(tr);
NavigableSet<String> val=tr.descendingSet();
System.out.println(val);
}
o/p-
[Nagpur, Manmad, Ahmednagr, Pune, Pune, Mumbai, Mumbai, Thane, Nashik]
[null, Bankok, Thane, Nagpur, Manmad, Pune, Ahmednagr, Nashik, Dubai, Mumbai]
[Dubai, Bankok, Nagpur, Manmad, Ahmednagr, Pune, Mumbai, Thane, Nashik, null]
[Ahmednagr, Manmad, Mumbai, Nagpur, Nashik, Pune, Thane]
[Thane, Pune, Nashik, Nagpur, Mumbai, Manmad, Ahmednagr]
