Multiple AsyncTasks load the same WebView

I'm trying to run many AsyncTasks to do loadData() on the same WebView. For example, I have 3 threads with 3 contents: "One", "Two", "Three" and a WebView with content "abc". (like the code below)

After 3 tasks finished, I want the WebView has content: "abcOneTwoThree". The idea of this code is that three threads will append its content to WebView at anytime, so the result could be "abcTwoOneThree" or "abcTwoThreeOne", etc ...

I read many concurrency articles but still don't understand how to implement this. This is my code. It just prints "abcThree".

public class UsingSameWebViewActivity extends Activity implements OnClickListener {
    private Button button1;
    private WebView webView;
    private String result;

    @Override
    public void onCreate(final Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        button1 = (Button)findViewById(R.id.button1);
        button1.setOnClickListener(this);
        webView = (WebView)findViewById(R.id.webView1);
        result = "abc";
    }

    @Override
    public void onClick(final View v) {
        final String[] contents = {"One", "Two", "Three"};
        for(int i = 0; i < 3; ++i) {
            final FooTask task = new FooTask(webView, result);
            task.execute(contents[i]);
        }
    }

    private class FooTask extends AsyncTask<String, Void, String> {
        private final WebView resultView;
        private String result;

        // This is what I try to make it work right.
        private synchronized String getResult() {
            return result;
        }

        public FooTask(final WebView resultView, final String result) {
            this.resultView = resultView;
            this.result = result;
        }

        @Override
        protected String doInBackground(final String... params) {
        // Do a long time work randomly then returns a string.
            return params[0];
        }

        @Override
        protected void onPostExecute(final String content) {
            result = getResult() + content;
            resultView.loadData(result, "text/html", "utf-8");
        }
    }
}

Remove the private String result; line from the Async Task class.