java - 验证多个输入字段时如何避免重复代码？

Question

如何在验证多个输入字段(如 TextField、DatePicker、ChoiceBoxes)时避免重复代码？下面这段代码属于 StageAddController 用来监听和验证输入的服务类。当焦点丢失且字段为空时，字段边框变为红色。

public void validateForEmptyTextField(TextField textField, PseudoClass errorClass){
    textField.focusedProperty().addListener((arg0, oldValue, newValue) -> {
        if (!newValue) { //when focus lost
            if(textField.getText().trim().isEmpty()){
                textField.pseudoClassStateChanged(errorClass, true);
            }
            else
                textField.pseudoClassStateChanged(errorClass, false);
        }
    });
}

public void validateForEmptyDatePicker (DatePicker datePicker, PseudoClass errorClass){
    datePicker.focusedProperty().addListener((arg0, oldValue, newValue) -> {
        if (!newValue) { //when focus lost
            if(datePicker.getValue() == null){
                datePicker.pseudoClassStateChanged(errorClass, true);
            }
            else
                datePicker.pseudoClassStateChanged(errorClass, false);
        }
    });
}

public void validateForEmptyChoiceBox (ChoiceBox<String > stringChoiceBox, PseudoClass errorClass){
    stringChoiceBox.focusedProperty().addListener((arg0, oldValue, newValue) -> {
        if (!newValue) { //when focus lost
            if(stringChoiceBox.getValue() == null){
                stringChoiceBox.pseudoClassStateChanged(errorClass, true);
            }
            else
                stringChoiceBox.pseudoClassStateChanged(errorClass, false);
        }
    });
}

Answer 1

可以通过引入一个泛型参数T来实现延伸 Node (1) 并传递 Predicate<T> (2):

public <T extends Node> void validateNodeForEmptyByPredicate(
    T node,
    PseudoClass errorClass,
    Predicate<T> predicate
) {
    node.focusedProperty().addListener((arg0, oldValue, newValue) -> {
        if (!newValue) {
            node.pseudoClassStateChanged(errorClass, predicate.test(node)); // *
        }
    });
}

• (1) 需要访问 focusedProperty方法;
• (2) 它会决定是否 T是空的，例如:
  • TextField小号 -> field -> field.getText().trim().isEmpty() ;
  • DatePicker小号 -> picker -> picker -> picker.getValue() == null ;
  • ChoiceBox es -> box -> box.getValue() == null .

我想重写下面的代码块(*)

if (predicate.test(node)) {
    node.pseudoClassStateChanged(errorClass, true);
} else {  
    node.pseudoClassStateChanged(errorClass, false);
}

进入:

node.pseudoClassStateChanged(errorClass, predicate.test(node));