I am trying to create a java wrapper for a perl program, whose essential purpose would be to forward the output of the perl program to the terminal window, and would forward input to the perl program's. Currently i can run the program and monitor the process by use of the Runtime.exec method. I use the process derived from this method to create a buffered writer. JavaScript String Reference Previous Next JavaScript Strings. A JavaScript string stores a series of characters like 'John Doe'. A string can be any text inside double or single quotes. The HTML wrapper methods return the string wrapped inside the appropriate HTML tag.
The wrapper class in Java provides the mechanism to convert primitive into object and object into primitive.
Since J2SE 5.0, autoboxing and unboxing feature convert primitives into objects and objects into primitives automatically. The automatic conversion of primitive into an object is known as autoboxing and vice-versa unboxing.
Use of Wrapper classes in Java
Java is an object-oriented programming language, so we need to deal with objects many times like in Collections, Serialization, Synchronization, etc. Let us see the different scenarios, where we need to use the wrapper classes.
- Change the value in Method: Java supports only call by value. So, if we pass a primitive value, it will not change the original value. But, if we convert the primitive value in an object, it will change the original value.
- Serialization: We need to convert the objects into streams to perform the serialization. If we have a primitive value, we can convert it in objects through the wrapper classes.
- Synchronization: Java synchronization works with objects in Multithreading.
- java.util package: The java.util package provides the utility classes to deal with objects.
- Collection Framework: Java collection framework works with objects only. All classes of the collection framework (ArrayList, LinkedList, Vector, HashSet, LinkedHashSet, TreeSet, PriorityQueue, ArrayDeque, etc.) deal with objects only.
The eight classes of the java.lang package are known as wrapper classes in Java. The list of eight wrapper classes are given below:
Primitive Type | Wrapper class |
---|---|
boolean | Boolean |
char | Character |
byte | Byte |
short | Short |
int | Integer |
long | Long |
float | Float |
double | Double |
Autoboxing
The automatic conversion of primitive data type into its corresponding wrapper class is known as autoboxing, for example, byte to Byte, char to Character, int to Integer, long to Long, float to Float, boolean to Boolean, double to Double, and short to Short.
Since Java 5, we do not need to use the valueOf() method of wrapper classes to convert the primitive into objects.
Wrapper class Example: Primitive to Wrapper
Output:
Unboxing
The automatic conversion of wrapper type into its corresponding primitive type is known as unboxing. It is the reverse process of autoboxing. Since Java 5, we do not need to use the intValue() method of wrapper classes to convert the wrapper type into primitives.
Wrapper class Example: Wrapper to Primitive
Output:
Java Wrapper classes Example
Output:
Custom Wrapper class in Java
Java Wrapper classes wrap the primitive data types, that is why it is known as wrapper classes. We can also create a class which wraps a primitive data type. So, we can create a custom wrapper class in Java.
Output:
Next TopicCall By Value and Call By Reference in Java
Linux Java Service Wrapper Example
This is a simple wrapper to run a Java program as service. You need to be a root user.
Intructions:
- Create a file under /etc/init.d/ with nano or vi and paste the example script below. ex. sudo vi /etc/init.d/mytestserv
- Modify the SERVICE_NAME, PATH_TO_JAR, and choose a PID_PATH_NAME for the file you are going to use to store your service ID.
- Write the file and give execution permisions ex. sudo chmod +x /etc/init.d/mytestserv
- Test that it runs ex. sudo service mytestserv start
- Test that it stops ex. sudo service mytestserv stop
- Test that it restarts ex. sudo service mytestserv restart
Copy the code example:
Modify if you need logs
If you need the output log replace the
2
lines for:
Known Issues
- Make sure your jar is not finishing execution by itself.
- Use the nohup java -jar Myjar.jar & to verify that it can work as a service.
- In Ubuntu use sudo update-rc.d mytestserv defaults if you want to run the service when the SO starts or sudo update-rc.d mytestserv disable to remove from startup.
- In Ubuntu 16+ init.d is deprecated, you will get a MyService.service not found there is another tutorial with systemd here