SortedSet Example

import java.util.Iterator;
import java.util.SortedSet;
import java.util.TreeSet;

public class SortedSetExample {

    public static void main(String[] args) {

        SortedSet<String> ss=new TreeSet<String>();

        ss.add("a");
        ss.add("e");
        ss.add("g");
        ss.add("b");
        ss.add("c");

        Iterator it=ss.iterator();

        while(it.hasNext())
        {
          String value=(String)it.next();

          System.out.println("Value :"+value);
        }
    }
}

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Remove elements from SortedMap

import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.SortedMap;
import java.util.TreeMap;

public class SortedMapRemoveExample {

    public static void main(String[] args) {

        SortedMap<Integer,String> sm=new TreeMap<Integer, String>();

        sm.put(new Integer(2), "Two");
        sm.put(new Integer(1), "One");
        sm.put(new Integer(4), "Four");
        sm.put(new Integer(3), "Three");
        sm.put(new Integer(5), "Five");

        // SortedMap remove object
        sm.remove(new Integer(4));

        Set s=sm.entrySet();

        Iterator i=s.iterator();

        while(i.hasNext())
        {
            Map.Entry m =(Map.Entry)i.next();

            int key = (Integer)m.getKey();
            String value=(String)m.getValue();

            System.out.println("Key :"+key+"  value :"+value);
        }
    }
}

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Remove elements from SortedSet

import java.util.Iterator;
import java.util.SortedSet;
import java.util.TreeSet;

public class SortedSetRemoveExample {

    public static void main(String[] args) {

        SortedSet<String> ss=new TreeSet<String>();

        ss.add("a");
        ss.add("e");
        ss.add("g");
        ss.add("b");
        ss.add("c");

        // remove SortedSet object
        ss.remove("g");

        Iterator it=ss.iterator();

        while(it.hasNext())
        {
          String value=(String)it.next();

          System.out.println("Value :"+value);
        }
    }
}

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Remove elements from Set

import java.util.Iterator;
import java.util.Set;
import java.util.TreeSet;

public class SetRemoveExample {

    public static void main(String[] args) {

        Set<String> s=new TreeSet<String>();

        s.add("b");
        s.add("a");
        s.add("d");
        s.add("c");

        // Set remove object
        s.remove("d");

        Iterator it=s.iterator();

        while(it.hasNext())
        {
          String value=(String)it.next();

          System.out.println("Value :"+value);
        }
    }
}

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Remove elements from Map

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

public class MapRemoveExample {

    public static void main(String[] args) {

        Map<Object,String> mp=new HashMap<Object, String>();

        mp.put(new Integer(2), "Two");
        mp.put(new Integer(1), "One");
        mp.put(new Integer(3), "Three");
        mp.put(new Integer(4), "Four");

        // remove map object
        mp.remove(new Integer(3)); // remove map by object

        Set s=mp.entrySet();

        Iterator it=s.iterator();

        while(it.hasNext())
        {
            Map.Entry m =(Map.Entry)it.next();

            int key=(Integer)m.getKey();

            String value=(String)m.getValue();

            System.out.println("Key :"+key+"  Value :"+value);
        }
    }
}

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Remove Element from ArrayList

import java.util.ArrayList;

public class RemoveArrayListElement {

    public static void main(String[] args) {

        ArrayList<String> arlist=new ArrayList<String>();

        //<E> it is return type of ArrayList

        arlist.add("First Element"); // adding element in ArrayList
        arlist.add("Second Element");
        arlist.add("Third Element");
        arlist.add("forth Element");
        arlist.add("fifth Element");

        // remove array list element by index number
        arlist.remove(3);

        // remove ArrayList element by Object value
        arlist.remove("fifth Element");

        // get elements of ArrayList
        for(int i=0;i<arlist.size();i++)
        {
            System.out.println("ArrayList Element "+i+" :"+arlist.get(i));
        }
    }
}

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Remove elements from List

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

public class ListRemoveExample {

    public static void main(String[] args) {

        List<String> ls=new ArrayList<String>();

        ls.add("one");
        ls.add("Three");
        ls.add("two");
        ls.add("four");

        // remove list object
        ls.remove(2); // remove by index number

        ls.remove("four"); // remove by object

        Iterator it=ls.iterator();

        while(it.hasNext())
        {
          String value=(String)it.next();

          System.out.println("Value :"+value);
        }
    }
}

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Compare HashSet,TreeSet and ArrayList by Example

import java.util.*;
import java.math.*;
public class NoDupsTest
{
  /* ---- HashSet approach (list order not maintained) ---- */
  public static void test_HashSet(ArrayList a_master)
  {
    ArrayList a = new ArrayList(a_master);
    long cur = System.currentTimeMillis();
    HashSet h = new HashSet(a);
    a.clear();
    a.addAll(h);
    long diff = System.currentTimeMillis()-cur;
    System.out.println("HashSet approach (no order) = "+diff);
  }
 
  /* ---- TreeSet approach (list order not maintained, but sorted) ---- */
  public static void test_TreeSet(ArrayList a_master)
  {
    ArrayList a = new ArrayList(a_master);
    long cur = System.currentTimeMillis();
    TreeSet t = new TreeSet(a);
    a.clear();
    Iterator iter = t.iterator();
    while (iter.hasNext())
      a.add(iter.next());
    long diff = System.currentTimeMillis()-cur;
    System.out.println(
      "TreeSet approach (sorted order) = "+diff+" ms");
  }
 
  /* ---- ArrayList and HashSet approach (order maintained) ---- */
  public static void test_HashSet_listOrder(ArrayList a_master)
  {
    ArrayList a = new ArrayList(a_master);
    long cur = System.currentTimeMillis();
    Set set = new HashSet();
    List newList = new ArrayList();
    for (Iterator iter = a.iterator(); iter.hasNext(); ) {
      Object element = iter.next();
      if (set.add(element))
        newList.add(element);
    }
    a.clear();
    a.addAll(newList);
    long diff = System.currentTimeMillis()-cur;
    System.out.println(
      "ArrayList/HashSet approach (list order) = "+diff+" ms");
  }
 
  /* ---- ArrayList and TreeSet approach ---- */
  public static void test_TreeSet_listOrder(ArrayList a_master)
  {
    ArrayList a = new ArrayList(a_master);
    long cur = System.currentTimeMillis();
    Set set = new TreeSet();
    List newList = new ArrayList();
    for (Iterator iter = a.iterator(); iter.hasNext(); ) {
      Object element = iter.next();
      if (set.add(element))
        newList.add(element);
    }
    a.clear();
    a.addAll(newList);
    long diff = System.currentTimeMillis()-cur;
    System.out.println(
      "ArrayList/TreeSet approach (list order) = "+diff+" ms");
  }
 
  public static void main(String[] args)
  {
    int num = Integer.parseInt(args[0]);
    int numUnique = Integer.parseInt(args[1]);
    /* Create master list */
    Random rnd = new Random();
    ArrayList masterList = new ArrayList();
    for (int i=0; i<num; i++) {
      masterList.add(new Integer((Math.abs(rnd.nextInt())%numUnique)));
    }
    /* Run tests */
    test_HashSet(masterList);
    test_TreeSet(masterList);
    test_HashSet_listOrder(masterList);
    test_TreeSet_listOrder(masterList);
  }
}

READ MORE - Compare HashSet,TreeSet and ArrayList by Example

Hashtable in java

// Demonstrate a Hashtable 
import java.util.*; 
class HTDemo { 
public static void main(String args[]) { 
Hashtable balance = new Hashtable(); 
Enumeration names; 
String str; 
double bal; 
balance.put("John Doe", new Double(3434.34)); 
balance.put("Tom Smith", new Double(123.22)); 
balance.put("Jane Baker", new Double(1378.00)); 
balance.put("Todd Hall", new Double(99.22)); 
balance.put("Ralph Smith", new Double(-19.08)); 
// Show all balances in hash table. 
names = balance.keys(); 
while(names.hasMoreElements()) { 
str = (String) names.nextElement(); 
System.out.println(str + ": " + 
balance.get(str)); 
} 
System.out.println(); 
// Deposit 1,000 into John Doe's account 
bal = ((Double)balance.get("John Doe")).doubleValue(); 
balance.put("John Doe", new Double(bal+1000)); 
System.out.println("John Doe's new balance: " + 
balance.get("John Doe")); 
} 
}

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How to use Iterator in Java

// Demonstrate iterators. 
import java.util.*; 
class IteratorDemo { 
public static void main(String args[]) { 
// create an array list 
ArrayList al = new ArrayList(); 
// add elements to the array list 
al.add("C"); 
al.add("A"); 
al.add("E"); 
al.add("B"); 
al.add("D"); 
al.add("F"); 
// use iterator to display contents of al 
System.out.print("Original contents of al: "); 
Iterator itr = al.iterator(); 
while(itr.hasNext()) {

    Object element = itr.next(); 
    System.out.print(element + " ");

} 
System.out.println(); 
// modify objects being iterated 
ListIterator litr = al.listIterator(); 
while(litr.hasNext()) {

    Object element = litr.next(); 
    litr.set(element + "+");

} 
System.out.print("Modified contents of al: "); 
itr = al.iterator();
while(itr.hasNext()) {

    Object element = itr.next(); 
    System.out.print(element + " ");

} 
System.out.println(); 
// now, display the list backwards 
System.out.print("Modified list backwards: "); 
while(litr.hasPrevious()) {

    Object element = litr.previous(); 
    System.out.print(element + " ");

} 
System.out.println(); 
} 
}

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HashMap example in Java

import java.util.*; 
class HashMapDemo { 
public static void main(String args[]) { 
// Create a hash map 
HashMap hm = new HashMap(); 
// Put elements to the map 
hm.put("John Doe", new Double(3434.34)); 
hm.put("Tom Smith", new Double(123.22)); 
hm.put("Jane Baker", new Double(1378.00)); 
hm.put("Todd Hall", new Double(99.22)); 
hm.put("Ralph Smith", new Double(-19.08)); 
// Get a set of the entries 
Set set = hm.entrySet(); 
// Get an iterator 
Iterator i = set.iterator(); 
// Display elements 
while(i.hasNext()) { 
Map.Entry me = (Map.Entry)i.next(); 
System.out.print(me.getKey() + ": "); 
System.out.println(me.getValue()); 
} 
System.out.println(); 
// Deposit 1000 into John Doe's account 
double balance = ((Double)hm.get("John Doe")).doubleValue(); 
hm.put("John Doe", new Double(balance + 1000)); 
System.out.println("John Doe's new balance: " + 
hm.get("John Doe")); 
} 
}

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ArrayList in java

// Demonstrate ArrayList. 
import java.util.*; 
class ArrayListDemo { 
public static void main(String args[]) { 
// create an array list 
ArrayList al = new ArrayList(); 
System.out.println("Initial size of al: " + 
al.size()); 
// add elements to the array list 
al.add("C"); 
al.add("A"); 
al.add("E"); 
al.add("B"); 
al.add("D"); 
al.add("F"); 
al.add(1, "A2"); 
System.out.println("Size of al after additions: " + 
al.size()); 
// display the array list 
System.out.println("Contents of al: " + al); 
// Remove elements from the array list 
al.remove("F"); 
al.remove(2); 
System.out.println("Size of al after deletions: " + 
al.size()); 
System.out.println("Contents of al: " + al); 
} 
}

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