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callable and future in java


The Callable interface available in java.util.concurrent package. It contains one method call() which returns the Future object. Return value can be retrieved after termination with get.
The Future object is used to check the status of a Callable. Result can be retrieved from the Callable once the thread is done.

Example

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
 
public class CallableAndFutureTest {
    public static void main(String args[]){
        ExecutorService es = Executors.newFixedThreadPool(3);
 
        Future<String> f1 = es.submit(new MyCallable("callable"));
        Future<String> f2 = es.submit(new MyCallable("future"));
        Future<String> f3 = es.submit(new MyCallable("codesjava"));
        Future<String> f4 = es.submit(new MyCallable("codesjava executor service"));
        Future<String> f5 = es.submit(new MyCallable("executors classes"));
 
        try {
            System.out.println("1. " + f1.get());
            System.out.println("2. " + f2.get());
            System.out.println("3. " + f3.get());
            if(f4.isDone()){
                System.out.println("4. " + f4.get());
            }else{
                System.out.println("waiting");
            }
            System.out.println("5. " + f5.get());
        } catch (Exception e) {
            e.printStackTrace();
        }
        es.shutdown();
    }
}
 
 
class MyCallable implements Callable<String> {
    String str;
    MyCallable(String str){
        this.str = str;
    }
    @Override
    public String call() throws Exception {
        System.out.println("In call method of Callable " + str);
        StringBuffer sb = new StringBuffer();
        return (sb.append("Length of string ").append(str).append(" is ").
                append(str.length())).toString();
 
    }
 
}

Output

In call method of Callable callable
In call method of Callable codesjava
In call method of Callable future
In call method of Callable codesjava executor service
In call method of Callable executors classes
1. Length of string callable is 8
2. Length of string future is 6
3. Length of string codesjava is 9
4. Length of string codesjava executor service is 26
5. Length of string executors classes is 17

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