再过一天,再纠结泛型。
我有一组具有以下继承树的Control
对象:
BaseControl
|_SimpleControl
|_MultipleControl
|_AutocompleteControl
|_SelectControl
对于此树中的每个非抽象对象,我想提供构建器,以便可以轻松创建这些对象。这是我到目前为止所拥有的:
BaseControlBuilder:
public abstract class BaseControlBuilder<C extends BaseControl, B extends BaseControlBuilder<C, B>> {
protected C control;
private B builder;
BaseControlBuilder() {
control = createObj();
builder = getThis();
}
public C build() { return control; }
protected abstract C createObj();
protected abstract B getThis();
}
SimpleControlBuilder:
public class SimpleControlBuilder<C extends SimpleControl, B extends SimpleControlBuilder<C, B>>
extends BaseControlBuilder<SimpleControl, SimpleControlBuilder<C, B>> {
public SimpleControlBuilder(final String id, final String caption,
final InputType controlType) {
super();
control.setId(id);
control.setCaption(caption);
control.setType(controlType);
}
public SimpleControlBuilder(final InputType controlType) {
this("", "", controlType);
}
public SimpleControlBuilder(final Enum<?> en, final InputType controlType) {
this(en.name(), en.toString(), controlType);
}
public SimpleControlBuilder<C, B> disabled() {
control.setDisabled(true);
return this;
}
@Override
protected SimpleControl createObj() {
return new SimpleControl();
}
@Override
protected SimpleControlBuilder<C, B> getThis() {
return this;
}
}
MultipleControlBuilder:
abstract class MultipleControlBuilder<C extends MultipleControl, B extends MultipleControlBuilder<C, B>>
extends SimpleControlBuilder<MultipleControl, MultipleControlBuilder<C, B>> {
MultipleControlBuilder(final InputType type) {
super(type);
}
MultipleControlBuilder(final String id, final String caption,
final InputType type) {
super(id, caption, type);
}
MultipleControlBuilder(final Enum<?> en, final InputType type) {
super(en, type);
}
public MultipleControlBuilder<C, B> multiple() {
((MultipleControl) control).setMultiple(true);
return this;
}
}
AutocompleteControlBuilder:
public class AutocompleteControlBuilder<C extends AutocompleteControl, B extends AutocompleteControlBuilder<C, B>>
extends MultipleControlBuilder<AutocompleteControl, AutocompleteControlBuilder<C, B>> {
public AutocompleteControlBuilder(final String url,
final AutocompleteType autocompleteType) {
this("", "", url, autocompleteType);
}
public AutocompleteControlBuilder(final String id,
final String caption, final String url,
final AutocompleteType autocompleteType) {
super(id, caption, InputType.AUTOCOMPLETE);
((AutocompleteControl) control).setAutocompleteUrl(url);
((AutocompleteControl) control).setAutocompleteType(autocompleteType);
}
public AutocompleteControlBuilder(final Enum<?> en, final String url,
final AutocompleteType autocompleteType) {
this(en.name(), en.toString(), url, autocompleteType);
}
@Override
protected AutocompleteControl createObj() {
return new AutocompleteControl();
}
@Override
protected AutocompleteControlBuilder<C, B> getThis() {
return this;
}
}
但令人惊讶的是,我得到了一些意想不到的结果。
例如,在下面的代码中,我必须将control
转换为MultipleControl
调用setter,尽管事实上C extends MultipleControl
...
此外,以下build()
方法调用:new AutocompleteControlBuilder<AutocompleteControl, AutocompleteControlBuilder>("url", AutocompleteType.STANDARD).build());
返回SimpleControl
而不是没有意义的AutocompleteControl
,因为我显式提供了类型参数。
最后一根稻草是,我试图实现的简洁和清晰的代码被丑陋的new AutocompleteControlBuilder<AutocompleteControl, AutocompleteControlBuilder>
构造函数调用所扼杀。谁能指出我解决这个问题的最佳实践?
好的,为了正确设置,您应该进行一些更改:
public class SimpleControlBuilder<C extends SimpleControl, B extends SimpleControlBuilder<C, B>>
extends BaseControlBuilder<SimpleControl, SimpleControlBuilder<C, B>> { // this should extend with the extension classes
public SimpleControlBuilder(final String id, final String caption,
final InputType controlType) {
super();
control.setId(id);
control.setCaption(caption);
control.setType(controlType);
}
public SimpleControlBuilder(final InputType controlType) {
this("", "", controlType);
}
public SimpleControlBuilder(final Enum<?> en, final InputType controlType) {
this(en.name(), en.toString(), controlType);
}
public SimpleControlBuilder<C, B> disabled() { // this should return B
control.setDisabled(true);
return this;
}
@Override
protected SimpleControl createObj() { // this should return C
return new SimpleControl();
}
@Override
protected SimpleControlBuilder<C, B> getThis() { // this should return B
return this;
}
}
所以这意味着
public abstract class SimpleControlBuilder<C extends SimpleControl, B extends SimpleControlBuilder<C, B>>
extends BaseControlBuilder<C, B> {
public SimpleControlBuilder(final String id, final String caption,
final InputType controlType) {
super();
control.setId(id);
control.setCaption(caption);
control.setType(controlType);
}
public SimpleControlBuilder(final InputType controlType) {
this("", "", controlType);
}
public SimpleControlBuilder(final Enum<?> en, final InputType controlType) {
this(en.name(), en.toString(), controlType);
}
public B disabled() {
control.setDisabled(true);
return getThis();
}
}
和
abstract class MultipleControlBuilder<C extends MultipleControl, B extends MultipleControlBuilder<C, B>>
extends SimpleControlBuilder<C, B> {
MultipleControlBuilder(final InputType type) {
super(type);
}
MultipleControlBuilder(final String id, final String caption,
final InputType type) {
super(id, caption, type);
}
MultipleControlBuilder(final Enum<?> en, final InputType type) {
super(en, type);
}
public B multiple() {
control.setMultiple(true);
return getThis();
}
}
和
public abstract class AutocompleteControlBuilder<C extends AutocompleteControl, B extends AutocompleteControlBuilder<C, B>>
extends MultipleControlBuilder<C, B>> {
public AutocompleteControlBuilder(final String url,
final AutocompleteType autocompleteType) {
this("", "", url, autocompleteType);
}
public AutocompleteControlBuilder(final String id,
final String caption, final String url,
final AutocompleteType autocompleteType) {
super(id, caption, InputType.AUTOCOMPLETE);
control.setAutocompleteUrl(url);
control.setAutocompleteType(autocompleteType);
}
public AutocompleteControlBuilder(final Enum<?> en, final String url,
final AutocompleteType autocompleteType) {
this(en.name(), en.toString(), url, autocompleteType);
}
}
这在 MultipleControl extends SimpleControl
和 AutocompleteControl extends MultipleControl
的情况下有效,并且您有SimpleControl
的具体扩展,这些扩展可以使用具有具体化参数的getThis()
返回自身。
public class SomeControlBuilder extends MultipleControlBuilder<SomeControl, SomeControlBuilder> {
public SomeControlBuilder(final InputType type) {
super(type);
}
public SomeControlBuilder(final String id, final String caption,
final InputType type) {
super(id, caption, type);
}
public SomeControlBuilder(final Enum<?> en, final InputType type) {
super(en, type);
}
@Override
protected SomeControlBuilder getThis() {
return this;
}
@Override
protected SomeControl createObj() {
return new SomeControl();
}
}