Java Future. Task Example Program Journal. Dev. Sometime back I wrote a post about Java Callable Future interfaces that we can use to get the concurrent processing benefits of threads as well as they are capable of returning value to the calling program. Future. Task is base concrete implementation of Future interface and provides asynchronous processing. It contains the methods to start and cancel a task and also methods that can return the state of the Future. Java Software Development and ObjectOriented Programming Paradigms A er learning the contents of this chapter, the reader would be able to understand. Java-Array-Sort-9.png' alt='What Is Object In Java With Example Program' title='What Is Object In Java With Example Program' />Task as whether its completed or cancelled. We need a callable object to create a future task and then we can use Java Thread Pool Executor to process these asynchronously. Lets see the example of Future. Task with a simple program. Since Future. Task requires a callable object, we will create a simple Callable implementation. Callable. public class My. Callable implements Callablelt String. Time. public My. Callableint time. In. Millis. this. Java-Method-Overriding-Examples-and-Concepts.png' alt='What Is Object In Java With Example Program' title='What Is Object In Java With Example Program' />Timetime. In. Millis. String call throws Exception. Thread. sleepwait. Time. return the thread name executing this callable task. Thread. current. Thread. Name. Here is an example of Future. This Java class example describes how class is defined and being used in Java language. Task method and its showing commonly used methods of Future. Task. package com. Execution. Exception. Executor. Service. Executors. import java. Collection_ListImplementation.png' alt='What Is Object In Java With Example Program' title='What Is Object In Java With Example Program' />Future. Task. import java. Time. Unit. import java. Timeout. Exception. Future. Task. Example. ExerciseOOP_Movable.png' alt='What Is Object In Java With Example Program' title='What Is Object In Java With Example Program' />String args. My. Callable callable. My. Callable1. 00. My. Callable callable. My. Callable2. 00. I have JSON object as follows member interests interestKeyDogs, interestKeyCats In Java I want to parse the above jsonobject and store the values in. Provide collection Swing controls. Commercial. ObjectOriented Programming 19962003 jGuru. All Rights Reserved. ObjectOriented Programming 1 ObjectOriented Programming Basics With Java. In this tutorial, it shows the use of java. Install Mcboot From Usb'>Install Mcboot From Usb. Comparable and java. Comparator to sort a Java object based on its property value. Fruit private. Future. Tasklt String future. Task. 1 new Future. Tasklt String callable. Future. Tasklt String future. Task. 2 new Future. Tasklt String callable. Executor. Service executor Executors. Fixed. Thread. Pool2. Task. 1. executor. Task. 2. while true. Task. 1. is. Done future. Task. 2. is. Done. System. out. printlnDone. Task. 1. is. Done. System. out. printlnFuture. Task. 1 outputfuture. Task. 1. get. System. Waiting for Future. Task. 2 to complete. String s future. Task. L, Time. Unit. MILLISECONDS. System. out. printlnFuture. Task. 2 outputs. Interrupted. Exception Execution. Exception e. e. Stack. Trace. catchTimeout. Exception e. do nothing. When we run above program, you will notice that it doesnt print anything for sometime because get method of Future. Task waits for the task to get completed and then returns the output object. There is an overloaded method also to wait for only specified amount of time and we are using it for future. Task. 2. Also notice the use of is. Done method to make sure program gets terminated once all the tasks are executed. Output of above program will be. Future. Task. 1 outputpool 1 thread 1. Waiting for Future. Task. 2 to complete. Waiting for Future. Task. 2 to complete. Waiting for Future. Task. 2 to complete. Waiting for Future. Task. 2 to complete. Waiting for Future. Task. 2 to complete. Future. Task. 2 outputpool 1 thread 2. As such there is no benefit of Future. Task but it comes handy when we want to override some of Future interface methods and dont want to implement every method of Future interface. Java Generics Example Tutorial Generic Method, Class, Interface. Java Genrics is one of the most important feature introduced in Java 5. If you have been working on Java Collections and with version 5 or higher, I am sure that you have used it. Generics in Java with collection classes is very easy but it provides a lot more features than just creating the type of collection and we will try to learn features of generics in this article. Manuale Per Patente Nautica. Understanding generics can become confusing sometimes if we go with jargon words, so I would try to keep it simple and easy to understand. We will look into below topics of generics in java. Generics in Java. Java Generic Class. Java Generic Interface. Java Generic Type. Java Generic Method. Java Generics Bounded Type Parameters. Java Generics and Inheritance. Java Generic Classes and Subtyping. Java Generics Wildcards. Java Generics Upper Bounded Wildcard. Java Generics Unbounded Wildcard. Java Generics Lower bounded Wildcard. Subtyping using Generics Wildcard. Java Generics Type Erasure. Generics in Java. Generics was added in Java 5 to provide compile time type checking and removing risk of Class. Cast. Exception that was common while working with collection classes. The whole collection framework was re written to use generics for type safety. Lets see how generics help us using collection classes safely. List list new Array. List. list. addabc. Integer5 OK. Object obj list. Class. Cast. Exception at runtime. Borland C Builder 6 Download Portable Software. String strString obj. Above code compiles fine but throws Class. Cast. Exception at runtime because we are trying to cast Object in the list to String whereas one of the element is of type Integer. After Java 5, we use collection classes like below. Listlt String list. Array. Listlt String java 7 Listlt String list. Array. Listlt. Integer5 compiler error. String str list. Class. Cast. Exception. Notice that at the time of list creation, we have specified that the type of elements in the list will be String. So if we try to add any other type of object in the list, the program will throw compile time error. Also notice that in for loop, we dont need type casting of the element in the list, hence removing the Class. Cast. Exception at runtime. Java Generic Class. We can define our own classes with generics type. A generic type is a class or interface that is parameterized over types. We use angle brackets lt to specify the type parameter. To understand the benefit, lets say we have a simple class as. Generics. Type. Old. Object t. public Object get. Object t. public static void mainString args. Generics. Type. Old type new Generics. Type. Old. type. Pankaj. String str String type. Class. Cast. Exception. Notice that while using this class, we have to use type casting and it can produce Class. Cast. Exception at runtime. Now we will use java generic class to rewrite the same class as shown below. Generics. Typelt T. T get. return this. T t. 1. public static void mainString args. Generics. Typelt String type new Generics. Typelt. Pankaj valid. Generics. Type type. Generics. Type raw type. Pankaj valid. Notice the use of Generics. Type class in the main method. We dont need to do type casting and we can remove Class. Cast. Exception at runtime. If we dont provide the type at the time of creation, compiler will produce a warning that Generics. Type is a raw type. References to generic type Generics. Typelt T should be parameterized. When we dont provide type, the type becomes Object and hence its allowing both String and Integer objects but we should always try to avoid this because we will have to use type casting while working on raw type that can produce runtime errors. Tip We can use Suppress. Warningsrawtypes annotation to suppress the compiler warning, check out java annotations tutorial. Also notice that it supports java autoboxing. Java Generic Interface. Comparable interface is a great example of Generics in interfaces and its written as. Comparablelt T. ToT o. In similar way, we can create generic interfaces in java. We can also have multiple type parameters as in Map interface. Again we can provide parameterized value to a parameterized type also, for example new Hash. Maplt String, Listlt String is valid. Java Generic Type. Java Generic Type Naming convention helps us understanding code easily and having a naming convention is one of the best practices of java programming language. So generics also comes with its own naming conventions. Usually type parameter names are single, uppercase letters to make it easily distinguishable from java variables. The most commonly used type parameter names are E Element used extensively by the Java Collections Framework, for example Array. List, Set etc. K Key Used in MapN Number. T Type. V Value Used in MapS,U,V etc. Java Generic Method. Sometimes we dont want whole class to be parameterized, in that case we can create java generics method. Since constructor is a special kind of method, we can use generics type in constructors too. Here is a class showing example of java generic method. Generics. Methods. Java Generic Method. T boolean is. EqualGenerics. Typelt T g. Generics. Typelt T g. String args. Generics. Typelt String g. Generics. Typelt. Pankaj. Generics. Typelt String g. Generics. Typelt. Pankaj. boolean is. Equal Generics. Methods. String is. Equalg. Equal Generics. Methods. Equalg. This feature, known as type inference, allows you to invoke a generic method as an ordinary method, without specifying a type between angle brackets. Compiler will infer the type that is needed. Notice the is. Equal method signature showing syntax to use generics type in methods. Also notice how to use these methods in our java program. We can specify type while calling these methods or we can invoke them like a normal method. Java compiler is smart enough to determine the type of variable to be used, this facility is called as type inference. Java Generics Bounded Type Parameters. Suppose we want to restrict the type of objects that can be used in the parameterized type, for example in a method that compares two objects and we want to make sure that the accepted objects are Comparables. To declare a bounded type parameter, list the type parameters name, followed by the extends keyword, followed by its upper bound, similar like below method. T extends Comparablelt T int compareT t. T t. 2. return t. Tot. 2. The invocation of these methods is similar to unbounded method except that if we will try to use any class that is not Comparable, it will throw compile time error. Bounded type parameters can be used with methods as well as classes and interfaces. Java Generics supports multiple bounds also, i. T extends A B C. In this case A can be an interface or class. If A is class then B and C should be interfaces. We cant have more than one class in multiple bounds. Java Generics and Inheritance. We know that Java inheritance allows us to assign a variable A to another variable B if A is subclass of B. So we might think that any generic type of A can be assigned to generic type of B, but its not the case. Lets see this with a simple program. Generics. Inheritance. String args. String str abc. Object obj new Object. String is a Object, inheritance in java.