如何解决为什么强烈鼓励使用构建器模式,而不是在 Java 中直接实现流畅的 API?
考虑以下构建器模式示例:
import java.util.Objects;
public class Vehicle {
private final String brand;
private final int wheels;
private final int doors;
private final int maxSpeed;
private Vehicle(Builder builder) {
this.brand = Objects.requireNonNull(builder.brand,"brand");
this.wheels = Objects.requireNonNull(builder.wheels,"wheels");
this.doors = Objects.requireNonNull(builder.doors,"doors");
this.maxSpeed = Objects.requireNonNull(builder.maxSpeed,"maxSpeed");
}
public static Builder builder() {
return new Builder();
}
public void display() {
System.out.println("brand = " + getBrand());
System.out.println("wheels = " + getWheels());
System.out.println("doors = " + getDoors());
System.out.println("maxSpeed = " + getMaxSpeed());
}
public String getBrand() {
return brand;
}
public int getWheels() {
return wheels;
}
public int getDoors() {
return doors;
}
public int getMaxSpeed() {
return maxSpeed;
}
public static class Builder {
private String brand;
private Integer wheels;
private Integer doors;
private Integer maxSpeed;
Builder() {
}
public Builder setBrand(String brand) {
this.brand = brand;
return this;
}
public Builder setWheels(int wheels) {
this.wheels = wheels;
return this;
}
public Builder setDoors(int doors) {
this.doors = doors;
return this;
}
public Builder setMaxSpeed(int maxSpeed) {
this.maxSpeed = maxSpeed;
return this;
}
public Builder of(Vehicle vehicle) {
this.brand = vehicle.brand;
this.wheels = vehicle.wheels;
this.doors = vehicle.doors;
this.maxSpeed = vehicle.maxSpeed;
return this;
}
public Vehicle build() {
return new Vehicle(this);
}
}
}
当我们创建一个 Vehicle
类型的对象时,我们有:
Vehicle vehicle = new Vehicle.Builder()
.setBrand("Mercedes")
.setWheels(4)
.setDoors(4)
.setMaxSpeed(250)
.build();
另一方面,可以在类 return this
的每个 setter 中简单地 Vehicle
,例如:
public class Vehicle {
private final String brand;
private final int wheels;
private final int doors;
private final int maxSpeed;
private Vehicle(String brand,int wheels,int doors,int maxSpeed){
this.brand = brand;
this.wheels = wheels;
this.doors = doors;
this.maxSpeed = maxSpeed;
}
public Vehicle() {
}
public String getBrand() {
return brand;
}
public int getWheels() {
return wheels;
}
public int getDoors() {
return doors;
}
public int getMaxSpeed() {
return maxSpeed;
}
public Vehicle setBrand(String brand) {
this.brand = brand;
return this;
}
public Vehicle setWheels(int wheels) {
this.wheels = wheels;
return this;
}
public Vehicle setDoors(int doors) {
this.doors = doors;
return this;
}
public Vehicle setMaxSpeed(int maxSpeed) {
this.maxSpeed = maxSpeed;
return this;
}
public void display() {
System.out.println("brand = " + getBrand());
System.out.println("wheels = " + getWheels());
System.out.println("doors = " + getDoors());
System.out.println("maxSpeed = " + getMaxSpeed());
}
}
我们可以通过以下方式创建一个 Vehicle
类型的对象:
Vehicle vehicle = new Vehicle();
vehicle.setBrand("Mercedes")
.setDoors(4)
.setMaxSpeed(250);
在我看来,第二种方法比传统的构建器模式生成的代码更少。尽管如此,我知道许多库使用构建器模式来代替。那么,与第二种方法相比,构建器模式的优点是什么?第二种方法实际上不那么复杂?
解决方法
与 fluent api 相比,构建器模式的一些好处:
- Builder 不仅可以返回 Vehicle 类,还可以返回 SomeClass 扩展 Vehicle
- 您可以将自定义复杂逻辑添加到构建方法中(验证、切换实现等)
- 没有必要的属性就不能创建 Vehicle
但是如果您不需要这些好处,那么使用您的方法绝对是正常的。一些图书馆使用它
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