具有继承的生成器模式支持泛型问题

Question

>我基于这个答案实现了模式 我有以下摘要配置：

public abstract class AbstractConfig {
public static abstract class Builder<B extends Builder<B>> {
private int calories = 0;
public Builder() {
}
public B setCalories(int calories) {
this.calories = calories;
return (B) this;
}
public abstract AbstractConfig build();
}
private int calories = 0;
protected AbstractConfig(final Builder builder) {
calories = builder.calories;
}
}

我有以下具体配置：

public class DialogConfig extends AbstractConfig {
public static class DialogConfigBuilder<B extends DialogConfigBuilder<B>> extends Builder<B> {
private double width;
private double height;
public DialogConfigBuilder() {
//does nothing.
}
public B setWidth(final double value) {
width = value;
return (B) this;
}
public B setHeight(final double value) {
height = value;
return (B) this;
}
public DialogConfig build() {
return new DialogConfig(this);
}
}
private final double width;
private final double height;
protected DialogConfig(final DialogConfigBuilder builder) {
super(builder);
width = builder.width;
height = builder.height;
}
public double getWidth() {
return width;
}
public double getHeight() {
return height;
}
}

这就是我使用它的方式

DialogConfig config = new DialogConfig.DialogConfigBuilder()
.setWidth(0)
.setCalories(0)
.setHeight(0) //X LINE
.build();

在 X 行我得到 - 找不到符号方法集高度。我的错误是什么？

编辑- 我将有一个扩展对话框配置，必须扩展对话框配置等。我的意思是会有其他子类。

Answer 1

首先将setCalories()更改为：

public Builder<B> setCalories(int calories) {
this.calories = calories;
return this;
}

摆脱那个演员和警告。现在仔细看看这个。您返回一个生成器。此代码不知道未来的子类。它只返回该基础构建器的一个实例。

因此，当您有该链式调用时：

.setHeight(0) .build();

这将返回该基础构建器。然后调用build()- 这将构建一个抽象配置。但是您希望将其分配给更具体的 DialogConfig。因此错误。

一个(丑陋的(解决方法：

DialogConfig.DialogConfigBuilder<?> builder = new DialogConfig.DialogConfigBuilder<>().setHeight(0);
builder.setCalories(0);
...config = builder.build();

还有一个解决方案- 通过再次返工setCalories()：

@SuppressWarnings("unchecked")
public <T extends B> T setCalories(int calories) {
this.calories = calories;
return (T) this;
}

修复编译错误;并允许链接setCalories()调用。摆脱投射/抑制的最后练习留给读者作为练习。

并记录在案 - "完整"解决方案，包括摆脱原始类型和其他警告的所有调整：

abstract class AbstractConfig {
public static abstract class Builder<B extends Builder<B>> {
private int calories = 0;
@SuppressWarnings("unchecked")
public <T extends B> T setCalories(int calories) {
this.calories = calories;
return (T) this;
}
public abstract AbstractConfig build();
}
private int calories = 0;
public int getCalories() { return calories; }
protected <B extends Builder<B>> AbstractConfig(final Builder<B> builder) {
calories = builder.calories;
}
}
final class DialogConfig extends AbstractConfig {
public static class DialogConfigBuilder<B extends DialogConfigBuilder<B>> extends Builder<B> {
private double width;    
private double height;
public DialogConfigBuilder<B> setWidth(final double value) {
width = value;
return this;
}
public DialogConfigBuilder<B> setHeight(final double value) {
height = value;
return this;
}
public DialogConfig build() {
return new DialogConfig(this);
}
}
private final double width;
private final double height;
protected <B extends DialogConfigBuilder<B>> DialogConfig(final DialogConfigBuilder<B> builder) {
super(builder);
width = builder.width;
height = builder.height;
}
public double getWidth() { return width; }
public double getHeight() { return height; }
}
public class Builders {
public static void main(String[] args) {
DialogConfig config = new DialogConfig.DialogConfigBuilder<>().setHeight(0).setCalories(0).build();
System.out.println(config);
}
}

Answer 2

我发现了我的错误。这就是我使用DialogConfigBuilder的方式

DialogConfig config = new DialogConfig.DialogConfigBuilder()
.setWidth(0)
.setCalories(0)
.setHeight(0) //X LINE
.build();

这就是我应该如何使用DialogConfigBuilder

DialogConfig config = new DialogConfig.DialogConfigBuilder<>()
.setWidth(0)
.setCalories(0)
.setHeight(0) //X LINE
.build();

在第二种情况下注意<>。