为建筑商模式释疑

Question

我正在学习builder模式,到目前为止,我了解到,它是用于初始化的常用模式的一个很好的替代方案：

>

伸缩构造函数模式

JavaBean模式

    public class Product
{
    private String color;
    private int price;

    public Product() {
    }

    public String getColor() {
        return color;
    }

    public void setColor(String color) {
        this.color = color;
    }

    public int getPrice() {
        return price;
    }

    public void setPrice(int price) {
        this.price = price;
    }

    public String toString() {
        return getColor() + "\n" + getPrice();
    }    
}

public class Builder
{
    private Product product;

    public Builder() {
        product = new Product();
    }
    public Builder withColor(String color) {        
        product.setColor(color);
        return this;
    }

     public Builder withPrice(int price) {        
        product.setPrice(price);
        return this;
    }
    public Product build() {
        return product;
    }
}**

public class Client
{

    public static void main(String[] args) {
        System.out.println(new Builder().withColor("Black").withPrice(11).build());
        System.out.println("-----------------------------------------------------");
        System.out.println(new Builder().withColor("Blue").withPrice(12).build());
    }
}

Answer 1

Builder模式对于创建不可变对象和避免几个具有可选参数的构造函数很有用。

IMO使用Builder模式来构建一个可以使用setter更新的POJO是没有用的。您只创建了一个额外的类。

根据使用的ORM框架，它可能不需要setter方法的存在。但仅通过反射为成员赋值。

public final class Product {
    private final String color;
    private final int price;

    public Product(Builder builder) {
        this.color = builder.getColor();
        this.price = builder.getPrice();
    }

    public String getColor() {
        return color;
    }

    public int getPrice() {
        return price;
    }

    public String toString() {
        return getColor() + "\n" + getPrice();
    }    
}

public final class Builder {

    private String color;
    private int price;

    public Builder() {
        // Assign any default values
    }

    public Builder color(String color) {        
        this.color = color;
        return this;
    }

    public Builder price(int price) {        
        this.price = price;
        return this;
    }

    protected String getColor() {
        return color;
    }

    protected int getPrice() {
        return price;
    }

    public Product build() {
        return new Product(this);
    }
}