Skip to main content

JAVA CLASSLOADER- Types, usages.

JVM loads library and classes dynamically only. Its on demand only.
A Class will be loaded only when needed and only once.

There can be system supported class loader and user supplied class loader.
When JVM starts it loads three type of class loader
1. Bootstrap loader - When system boots. Loads from jre_home/lib/
2. External class loader - Loads from jre_home/lib/ext.
3. System Class loader - Loads classes from system property CLASSPATH.


Besides this user can provide their own class loader which is pretty easy to implement in Java.
User supplied loader will work in conjunction with other loader i.e. system loader too.

Some of the examples are:

1. Load library at runtime from http resources. Example scripting classes, bean classes.
2. Can load encrypted class files with new class loader.
3. Modify the byte code.

Application Container loads classes from deployed WAR or EAR files using a tree of class loaders.

Comments

Popular posts from this blog

[PUZZLE] ELEPHANT AND BANANA PUZZLE

A merchant has bough some 3000 banana from market and want to bring them to his home which is 1000 km far from Market. He have a elephant which can carry maximum of 1000/- banana at time. That could have been easy but this elephant is very shrewd and he charges 1 banana for every one kilometer he travel. Now we have to maximise number of banana which should reach to home. Solution: At present we are at 0th km with 3000 banana and elephant. Lets see if elephant have to shift all the 3000 banana and elephant by 1 km. For 1 km shift: Take first 1000 banana and drop at 1st km. 2 banana consumed. One banana each for to and fro. Second  1000 banana and drop at 1st km. 2 banana consumed. Third 1000 banana and reach at 1st km. 1 banana consumed. So all in all total 5 banana will be consumed if we shift a kilometer. But that's not all, our total banana number are also reducing so we may have to reduce the number of turns too. And this will happen once we have reduced the b

Complete the Tour

Given a circular road and a set of petrol pumps located at distances d1 d2 ... dn away from each other and supplying p1 p2 p3 ... pn amounts of fuel and your vehicle has a mileage of 1km/l. Determine the feasibility of going around the path starting with zero fuel. Find a point from which you can start and complete the cycle given that you have zero initial fuel. This will be O(n) algorithm. Start from a random node say i...check till the last node it reach. Two case: 1: Either it reach to last node. And current node i is result. 2. It stopped at node j. Then start from node j+1. to find where we can reach all the node by above algorithm. No Node from i to j can complete the traversal, because each node will start with 0 petrol. While traversing from i we always reached that node >= 0. So that condition is already checked.

[JAVA] Evil Null

Elvis operator could have been a good use here. But unfortunately have been decline till now. Its used to say "?." Operate only if not null. Class A {  public B getB() {    return new B(); } } public void test( A a) {     if ( a != null  )         return a.getB();  } Above method would be replaced with public void test ( A a) {      return a?.getB();  } Unfortunately its still some time we can see some think like that. So till that we have to live with two choices: 1. Check for null. 2. Use the Null Object Pattern. So we all know that how to check for null objects and believe me i had real long chain of checking null. Second way can be useful but if this chain is pretty long its can be tiresome to have null object for all the hierarchy Null Object means there will be definition of class A (mostly derived from same interface.) and will have dummy methods which will nullify any call to these methods.