寫Java一陣子都知道，最常出現的錯誤例外就是NullPointerException，而為了避免出現這個例外，所以程式中經常使用if else先判斷物件是否為null後，才會去呼叫物件的方法。
例如下面範例的物件類別為Computer與VideoCard
Computer
public class Computer {
private VideoCard videoCard;
public VideoCard getVideoCard() {
return videoCard;
}
public void setVideoCard(VideoCard videoCard) {
this.videoCard = videoCard;
}
}
VideoCard
public class VideoCard {
private String videoCardName;
public String getVideoCardName() {
return videoCardName;
}
public void setVideoCardName(String videoCardName) {
this.videoCardName = videoCardName;
}
}
產生Computer的工廠類。
ComputerFactory
public class ComputerFactory {
public Computer getComputer() {
String videoCardName = "Geforce RTX 2080 Ti";
Computer computer = new Computer();
VideoCard videoCard = new VideoCard();
videoCard.setVideoCardName(videoCardName);
computer.setVideoCard(videoCard);
return computer;
}
}
isNivida()方法原本使用if else如下。
Main
public class Main {
public static void main(String[] args) {
ComputerFactory factory = new ComputerFactory();
Computer computer = factory.getComputer();
System.out.println(isNvidia(computer));
}
public static boolean isNvidia(Computer computer) {
if (computer != null) {
VideoCard videoCard = computer.getVideoCard();
if (videoCard != null) {
String videoCardName = videoCard.getVideoCardName();
if (videoCardName != null) {
if (videoCardName.contains("Geforce")) {
return true;
}
}
}
}
return false;
}
}
改用Java 8的Optional來寫。
Main
public class Main {
public static void main(String[] args) {
ComputerFactory factory = new ComputerFactory();
Computer computer = factory.getComputer();
System.out.println(isNvidia(computer));
}
public boolean isNvidia(Computer computer) {
return Optional.ofNullable(computer)
.map(Computer::getVideoCard) // 若computer不是empty，返回Computer.getVideoCard()
.map(VideoCard::getVideoCardName) // 若c.getVideoCard()不是empty，返回VideoCard.getVideoCardName()
.filter(s -> s.contains("Geforce")).isPresent(); // 若filter()滿足，返回true，否則返回false。
}
}
還是覺得不好懂，也很不惜慣這種寫法。
參考：
沒有留言:
張貼留言