JAVA EXAMPLE PROGRAMS

JAVA EXAMPLE PROGRAMS

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Proxy Design Pattern in java


Proxy design pattern is very simple, but very effective. Proxy pattern provide a surrogate or placeholder for another object to control access to it.

Proxy design pattern allows us to create a wrapper class over real object. Wrapper class which is proxy, controls access to real object so in turn we can add extra functionalities to real object without changing real object's code. A very simple real life scenario is our office internet, which restricts few site access. The proxy first checks the host you are connecting to, if it is not part of restricted site list, then it connects to the real internet.

There are four common situations in which the Proxy pattern is applicable:

1) A remote proxy provides a local representative for an object that resides in a different address space. This is what the "stub" code in RPC and CORBA provides.

2) A virtual proxy is a placeholder for "expensive to create" objects. The real object is only created when a client first requests/accesses the object.

3) A protective proxy controls access to a sensitive master object. The "surrogate" object checks that the caller has the access permissions required prior to forwarding the request.

4) A smart proxy interposes additional actions when an object is accessed.

Here is the code for proxy pattern.

package com.java2novice.dp.proxy;

public interface Internet {

	public void connectTo(String host) throws Exception;
}

Real internet class

package com.java2novice.dp.proxy;

public class RealInternet implements Internet {

	@Override
	public void connectTo(String host) {
		System.out.println("Connecting to "+host);
	}
}

Proxy internet class

package com.java2novice.dp.proxy;

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

public class InternetProxy implements Internet {

	private Internet internet = new RealInternet();
	private static List<String> restrictedSites;
	
	static {
		restrictedSites = new ArrayList<String>();
		restrictedSites.add("jumbxyz.com");
		restrictedSites.add("testme.com");
		restrictedSites.add("adult-site.com");
		restrictedSites.add("bad-site.com");
	}
	
	@Override
	public void connectTo(String host) throws Exception {
		
		if(!restrictedSites.contains(host.toLowerCase())){
			internet.connectTo(host);
		}
		throw new Exception("Company restricted this site view");

	}

}

proxy demo class

package com.java2novice.dp.proxy;

public class ProxyDemo {

	public static void main(String a[]){
		
		Internet intConn = new InternetProxy();
		try {
			intConn.connectTo("java2novice.com");
			intConn.connectTo("adult-site.com");
		} catch (Exception e) {
			System.out.println(e.getMessage());
		}
	}
}

Output:
Connecting to java2novice.com
Company restricted this site view
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Java design pattern examples

  1. Factory Pattern
  2. Abstract Factory Pattern
  3. Builder Design Pattern
  4. Prototype Pattern
  5. Adapter Pattern
  6. Composite Pattern
  7. Proxy Pattern
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Preemptive scheduling Vs Time slicing?
Preemptive scheduling: The highest priority task executes until it enters the waiting or dead states or a higher priority task comes into existence.

Time slicing: A task executes for a predefined slice of time and then reenters the pool of ready tasks. The scheduler then determines which task should execute next, based on priority and other factors.
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Reference: Java™ Platform Standard Ed. 7 - API Specification | Java is registered trademark of Oracle.
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