Java How to Program, Early Objects, 11th Edition

17.16 Lambda Event Handlers

In Section 12.5.5, you learned how to implement an event handler using an anonymous inner class. Event-listener interfaces with one abstract method—like ChangeListener—are functional interfaces. For such interfaces, you can implement event handlers with lambdas. For example, the following Slider event handler from Fig. 12.23:

tipPercentageSlider.valueProperty().addListener(  
   new ChangeListener<Number>() {  
      @Override  
      public void changed(ObservableValue<? extends Number> ov,  
         Number oldValue, Number newValue) {  
         tipPercentage =  
            BigDecimal.valueOf(newValue.intValue() / 100.0);  
         tipPercentageLabel.setText(percent.format(tipPercentage));
      }
   }
);

can be implemented more concisely with a lambda as

tipPercentageSlider.valueProperty().addListener( ...