## JAVA EXAMPLE PROGRAMS

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# Program: Write a program to find perfect number or not.

 Description: ```A perfect number is a positive integer that is equal to the sum of its proper positive divisors, that is, the sum of its positive divisors excluding the number itself. Equivalently, a perfect number is a number that is half the sum of all of its positive divisors. The first perfect number is 6, because 1, 2 and 3 are its proper positive divisors, and 1 + 2 + 3 = 6. Equivalently, the number 6 is equal to half the sum of all its positive divisors: ( 1 + 2 + 3 + 6 ) / 2 = 6.```

 Code: ```package com.java2novice.algos; public class IsPerfectNumber { public boolean isPerfectNumber(int number){ int temp = 0; for(int i=1;i<=number/2;i++){ if(number%i == 0){ temp += i; } } if(temp == number){ System.out.println("It is a perfect number"); return true; } else { System.out.println("It is not a perfect number"); return false; } } public static void main(String a[]){ IsPerfectNumber ipn = new IsPerfectNumber(); System.out.println("Is perfect number: "+ipn.isPerfectNumber(28)); } }```

 Output: ```28 It is a perfect number Is perfect number: true```

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Difference between Enumeration and Iterator
The functionality of Enumeration and the Iterator are same. You can get remove() from Iterator to remove an element, while while Enumeration does not have remove() method. Using Enumeration you can only traverse and fetch the objects, where as using Iterator we can also add and remove the objects. So Iterator can be useful if you want to manipulate the list and Enumeration is for read-only access.
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