如何正确使用持有人的泛型 [英] How to use generics properly for a Holder

问题描述

我试图为我的应用程序中使用的不同对象创建一个Holder类，直到某种程度上，此代码才能正常工作，但构建器模式对于可选字段工作正常，但我想这个持有者可以被重构为接受任意数量的参数

  package pojos; 
 
公开课持有人< T，R，S，U> {
 private final T t; 
 private final R r; 
 
 private final S s; 
 private final U u; 
 
 
私人持有人（最终建造者< T，R，S，U>建造者）{
 this.t = builder.t; 
 this.r = builder.r; 
 this.s = builder.s; 
 this.u = builder.u; 
} 
 
 
 public T getField1（）{
 return this.t; 
} 
 
 public R getField2（）{
 return this.r; 
} 
 
 public S getField3（）{
 return this.s; 
} 
 
 public U getField4（）{
 return this.u; 
} 
 
 
 public static class Builder< T，R，S，U> {
 private T t; 
私人R r; 
私人S s; 
私人U u; 
 
 
 public Builder field1（final T t）{
 this.t = t; 
返回此; 
} 
 
 public Builder field2（final R r）{
 this.r = r; 
返回此; 
} 
 
 public Builder field3（final S s）{
 this.s = s; 
返回此; 
} 
 
 public Builder field4（final U u）{
 this.u = u; 
返回此; 
} 
 
公共持有人< T，R，S，U> build（）{
返回新的Holder<>（this）; 
} 
 
 public Builder< T，R，S，U>复制（最终Holder< T，R，S，U> rowMappingsHolder）{
 this.t = rowMappingsHolder.getField1（）; 
 this.r = rowMappingsHolder.getField2（）; 
 this.s = rowMappingsHolder.getField3（）; 
 this.u = rowMappingsHolder.getField4（）; 
返回此; 
} 
 
 
} 
  

}}使用示例：

 受保护的Holder< Row，Map< Integer， String>，Void，Void> getRowMapHolder（Row row，Map< Integer，String> map）{
 return（Holder< Row，Map< Integer，String> ;, Void，Void>）new Holder.Builder< Row，Map< Integer，String> ;, Void>（）.field1（row）.field2（map）.build（）; 
 
 $ / code> 

任何想法？



问候

〜Marco

解决方案

感谢Andy的评论和Google Autovalue是一个很好的解决方案：

所以我们可以创建不同的有意义的类，没有更多的field1，field2...

  package pojos; 
 
导入com.google.auto.value.AutoValue; 
 import org.apache.poi.ss.usermodel.Row; 
 
 import java.util.Map; 
 
 @AutoValue 
公共抽象类RowMapHolder {
 
 public abstract Row row（）; 
 
 public abstract Map< Integer，String>映射（）; 
 $ b $ public static RowMapHolder create（Row row，Map< Integer，String> mapping）{
 return new AutoValue_RowMapHolder（row，mapping）; 
} 
 
} 
  

或

  package pojos; 
 
导入com.google.auto.value.AutoValue; 
 
 import java.util.List; 
 import java.util.Map; 
 
 @AutoValue 
 public abstract class KeyValuesMapHolder {
 
 public abstract List< KeyValue< String，String>>键值（）; 
 public abstract Map< Integer，String>映射（）; 
 $ b $ public static KeyValuesMapHolder create（List< KeyValue< String，String>> keyValues，Map< Integer，String>映射）{
返回新的AutoValue_KeyValuesMapHolder（keyValues，mapping）; 
} 
 
} 
  

I am trying to create a Holder class for different objects to be used in my application, I ended up with this code that works fine until some extent, the builder pattern works fine for the optional fields, but I guess this holder could be refactored to accept any arbitrarily number of parameter

package pojos;

public class Holder<T, R, S, U> {
private final T t;
private final R r;

private final S s;
private final U u;


private Holder(final Builder<T, R, S, U> builder) {
    this.t = builder.t;
    this.r = builder.r;
    this.s = builder.s;
    this.u = builder.u;
}


public T getField1() {
    return this.t;
}

public R getField2() {
    return this.r;
}

public S getField3() {
    return this.s;
}

public U getField4() {
    return this.u;
}


public static class Builder<T, R, S, U> {
    private T t;
    private R r;
    private S s;
    private U u;


    public Builder field1(final T t) {
        this.t = t;
        return this;
    }

    public Builder field2(final R r) {
        this.r = r;
        return this;
    }

    public Builder field3(final S s) {
        this.s = s;
        return this;
    }

    public Builder field4(final U u) {
        this.u = u;
        return this;
    }

    public Holder<T, R, S, U> build() {
        return new Holder<>(this);
    }

    public Builder<T, R, S, U> copy(final Holder<T, R, S, U> rowMappingsHolder) {
        this.t = rowMappingsHolder.getField1();
        this.r = rowMappingsHolder.getField2();
        this.s = rowMappingsHolder.getField3();
        this.u = rowMappingsHolder.getField4();
        return this;
    }


}

}

Example of usage:

protected Holder<Row, Map<Integer, String>, Void, Void> getRowMapHolder(Row row, Map<Integer,String> map) {
    return (Holder<Row, Map<Integer, String>, Void, Void>) new Holder.Builder<Row, Map<Integer, String>,Void, Void>().field1(row).field2(map).build();
}

Any ideas?

Regards

~Marco

解决方案

Thanks to Andy's comment and Google Autovalue, a good solution arose:

So we can create different classes that have meaning, no more "field1", "field2"...

package pojos;

import com.google.auto.value.AutoValue;
import org.apache.poi.ss.usermodel.Row;

import java.util.Map;

@AutoValue
public abstract class RowMapHolder {

    public abstract Row row();

    public abstract Map<Integer,String> mapping();

    public static RowMapHolder create(Row row, Map<Integer, String> mapping) {
        return new AutoValue_RowMapHolder(row, mapping);
    }

}

or

package pojos;

import com.google.auto.value.AutoValue;

import java.util.List;
import java.util.Map;

@AutoValue
public abstract class KeyValuesMapHolder {

    public abstract List<KeyValue<String,String>> keyValues();
    public abstract Map<Integer,String> mapping();

    public static KeyValuesMapHolder create(List<KeyValue<String, String>> keyValues, Map<Integer, String> mapping) {
        return new AutoValue_KeyValuesMapHolder(keyValues, mapping);
    }

}

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