Predicate used in Selenium WebDriver wait

predicate.java

public void authenticate() {
    this.authenticateButton.click();
    new WebDriverWait(driver, 30).until(authenticated());
}
 
private Predicate<WebDriver> authenticated() {
    return new Predicate<WebDriver>() {
        @Override public boolean apply(WebDriver driver) {
            return isAuthenticated();
        }
    };
}
 
 //delegate method here
private boolean isAuthenticated() {
    return (Boolean) executor().executeScript("return authenticated;");
}
private JavascriptExecutor executor() {
    return (JavascriptExecutor) driver;
}

http://howtodoinjava.com/2014/04/04/how-to-use-predicate-in-java-8/