Prior to Java 7, there was no auto resource management, we open the resource in a try block and close the resource in finally block. For example:

try{

//open resources

}catch(IOException){

//Exception handling

}finally{

//close resource

}

In the above approach there were few drawbacks:

1. It causes memory leaks and performance issue if the developer forgot to close the resource.
2. Finally block will always be executed, it doesn’t matter if the exception is thrown from the try block. It means, it tries to close the resource in finally block, even if it doesn’t exist which again cause an exception to be thrown from finally block.
3. Exception thrown from finally block will be propagated up the call stack, though exception from try block is more relevant.

try-with-resource
In Java 7, a new approach called “try-with-resources” is introduced for auto resource management. In this when try block finishes, it automatically closes the resource.

Here is an example for try-with-resource construct:

private static void readFile() throws IOException {

try(FileInputStream input = new FileInputStream("file.txt")) {

int data = input.read();

while(data != -1){

System.out.print((char) data);

data = input.read();

}

}

}

try-with-resource using multiple resources
We can use multiple resources in try-with-resource block, it will automatically close both the resources when program finish executing try block.

private static void readFile() throws IOException {

try(  FileInputStream input = new FileInputStream("file.txt");

BufferedInputStream bufferedInput = new BufferedInputStream(input)

) {

int data = bufferedInput.read();

while(data != -1){

System.out.print((char) data);

data = bufferedInput.read();

}

}

}

The resources are closed in reverse order of they are declared inside the try. BufferedInputStream will be closed first, then FileInputStream.
 
AutoCloseable Custom implementation
Java 7 has introduced an interface java.lang.AutoCloseable. To use any resource in try-with-resource block, it must implement the AutoCloseable interface. We can also implement java.lang.AutoCloseable interface in our own classes and use them with the try-with-resources construct.
AutoCloseable interface only has one method class close(). Here is the AutoCloseable interface:

public interface AutoCloseable {

public void close() throws Exception;

}

 
Exception handling with try-with-resource:
If one or more exceptions are thrown by try block in try-with-resources, the exceptions thrown are suppressed exception.
Java added an constructor and two methods in Throwable class to deal with suppressed exceptions. We can get these exceptions by using the getSuppress() method of Throwable class.

Advantages of using try-with-resource construct:

1. Auto resource management.
2. More readable code.
3. No need of finally block just to close the resource.
4. Meaning & relevant exceptions.

The post Java Try with Resources appeared first on Manish Sanger.

$sudo apt-get purge openjdk*

If you installed java 7 earlier and having problem with java then you have to do the following to remove it:

$sudo rm /var/lib/dpkg/info/oracle-java7-installer*

$sudo apt-get purge oracle-java7-installer*

$sudo rm /etc/apt/sources.list.d/*java*

$sudo apt-get update

Installing Oracle Java7 on Ubuntu 12.04 LTS:

$sudo add-apt-repository ppa:webupd8team/java

$sudo apt-get update

$sudo apt-get install oracle-java7-installer

You will be prompted couple of times for permissions and Oracle Policy agreement [You must be agreed to Oracle policies to install Java :-)].

That’s it! Now you have Oracle Java7 installed on your Ubuntu 12.04 environment, to check the Java version run the following on terminal:

$java -version

java version "1.7.0_17"

Java(TM) SE Runtime Environment (build 1.7.0_17-b02)

Java HotSpot(TM) 64-Bit Server VM (build 23.7-b01, mixed mode)

Or You can check the java version by searching java in Ubuntu dashboard.

Oracle Java 7 plugin Control Panel -> General Tab -> About

The post Install Java7 on Linux (Ubuntu 12.04) appeared first on Manish Sanger.