return String from a callback - Java

user_806747 0
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does anyone know how I can solve the following problem. I want to return a String from a callback, but I get only "The final local variable s cannot be assigned, since it is defined in an enclosing type", because of final. 

 public String getConstraint(int indexFdg) {
    final String s;
    AsyncCallback<String> callback = new AsyncCallback<String>() {
        public void onFailure(Throwable caught) {
            caught.printStackTrace();
        }

        public void onSuccess(String result) {
            s = result;
        }
    };
    SpeicherService.Util.getInstance().getConstraint(indexFdg, callback);
    return s;
    }
return callback java string
2 Answers

An alternative workaround is to define a new class, called SyncResult

public class SyncResult {
    private static final long TIMEOUT = 20000L;
    private String result;

    public String getResult() {
        long startTimeMillis = System.currentTimeMillis();
        while (result == null && System.currentTimeMillis() - startTimeMillis < TIMEOUT) {
            synchronized (this) {
                try {
                    wait(TIMEOUT);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }
        return result;
    }

    public void setResult(String result) {
        this.result = result;
        synchronized (this) {
            notify();
        }
    }
}

Then change your code to this

public String getConstraint(int indexFdg) {
    final SyncResult syncResult = new SyncResult();
    AsyncCallback<String> callback = new AsyncCallback<String>() {
        public void onFailure(Throwable caught) {
            caught.printStackTrace();
        }

        public void onSuccess(String result) {
            syncResult.setResult(result);
        }
    };
    SpeicherService.Util.getInstance().getConstraint(indexFdg, callback);
    return syncResult.getResult();
}

The getResult() method will be blocked until setResult(String) method been called or the TIMEOUT reached.

user_51861530
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