🎩 Неизменяемость в Java 🔥 Упрощена

import java.util.Date;
import java.util.List;
import java.util.Objects;

public class OldModel {

    private String fieldA;
    private Date fieldB;
    private Long fieldC;
    private List fieldD;

    public OldModel() {
    }

    public String getFieldA() {
        return fieldA;
    }

    public void setFieldA(String fieldA) {
        this.fieldA = fieldA;
    }

    public Date getFieldB() {
        return fieldB;
    }

    public void setFieldB(Date fieldB) {
        this.fieldB = fieldB;
    }

    public Long getFieldC() {
        return fieldC;
    }

    public void setFieldC(Long fieldC) {
        this.fieldC = fieldC;
    }

    public List getFieldD() {
        return fieldD;
    }

    public void setFieldD(List fieldD) {
        this.fieldD = fieldD;
    }

    @Override
    public String toString() {
        return "OldModel{" +
                "fieldA='" + fieldA + '\'' +
                ", fieldB=" + fieldB +
                ", fieldC=" + fieldC +
                ", fieldD=" + fieldD +
                '}';
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        OldModel oldModel = (OldModel) o;
        return Objects.equals(getFieldA(), oldModel.getFieldA()) &&
                Objects.equals(getFieldB(), oldModel.getFieldB()) &&
                Objects.equals(getFieldC(), oldModel.getFieldC()) &&
                Objects.equals(getFieldD(), oldModel.getFieldD());
    }

    @Override
    public int hashCode() {
        return Objects.hash(getFieldA(), getFieldB(), getFieldC(), getFieldD());
    }
}

-public class OldModel {
+public final class OldModel {

-    private String fieldA;
-    private Date fieldB;
-    private Long fieldC;
-    private List fieldD;
+    private final String fieldA;
+    private final Date fieldB;
+    private final Long fieldC;
+    private final List fieldD;

-    public OldModel() {
+    public OldModel(
+            final String fieldA,
+            final Date fieldB,
+            final Long fieldC,
+            final List fieldD) {
+        this.fieldA = fieldA;
+        this.fieldB = fieldB;
+        this.fieldC = fieldC;
+        this.fieldD = fieldD;
     }

-    public void setFieldA(String fieldA) {
-        this.fieldA = fieldA;
-    }
.
. // Remove all the setters
.

+   public Date getFieldB() {
+       return new Date(fieldB.getTime()); // Easy to forget about this :(
+   }
+
+   public List getFieldD() {
+       return Collections.unmodifiableList(fieldD); // This is not great :(
+   }

import java.util.Collections;
import java.util.Date;
import java.util.List;
import java.util.Objects;

public final class OldModel {

    private final String fieldA;
    private final Date fieldB;
    private final Long fieldC;
    private final List fieldD;

    public OldModel(
            final String fieldA,
            final Date fieldB,
            final Long fieldC,
            final List fieldD) {
        this.fieldA = fieldA;
        this.fieldB = fieldB;
        this.fieldC = fieldC;
        this.fieldD = fieldD;
    }

    public String getFieldA() {
        return this.fieldA;
    }

    public Date getFieldB() {
        return new Date(this.fieldB.getTime()); // Easy to forget about this :(
    }

    public Long getFieldC() {
        return this.fieldC;
    }

    public List getFieldD() {
        return Collections.unmodifiableList(this.fieldD); // This is not great :(
    }

    // toSting, equals and hashCode omitted
}

    org.immutables
    value
    2.8.3
    provided

import org.immutables.value.Value;

import java.util.Date;
import java.util.List;

@Value.Immutable
public interface NewModel {

    String fieldA();

    Date fieldB();

    Long fieldC();

    List fieldD();
}

public class App {
    public static void main(String[] args) {
        final ImmutableNewModel model = ImmutableNewModel.builder()
                .fieldA("A")
                .fieldB(new Date())
                .fieldC(1L)
                .addFieldD("a", "b", "d")
                .addFieldD("e")
                .build();
        System.out.println(model);
    }
}

NewModel{fieldA=A, fieldB=Sat Apr 11 15:53:26 PDT 2020, fieldC=1, fieldD=[a, b, d, e]}

package com.groupon.api.talks;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Date;
import java.util.List;
import java.util.Objects;
import org.immutables.value.Generated;

/**
 * Immutable implementation of {@link NewModel}.
 * 

 * Use the builder to create immutable instances:
 * {@code ImmutableNewModel.builder()}.
 */
@Generated(from = "NewModel", generator = "Immutables")
@SuppressWarnings({"all"})
@javax.annotation.Generated("org.immutables.processor.ProxyProcessor")
public final class ImmutableNewModel implements NewModel {
  private final String fieldA;
  private final Date fieldB;
  private final Long fieldC;
  private final List fieldD;

  private ImmutableNewModel(
      String fieldA,
      Date fieldB,
      Long fieldC,
      List fieldD) {
    this.fieldA = fieldA;
    this.fieldB = fieldB;
    this.fieldC = fieldC;
    this.fieldD = fieldD;
  }

  /**
   * @return The value of the {@code fieldA} attribute
   */
  @Override
  public String fieldA() {
    return fieldA;
  }

  /**
   * @return The value of the {@code fieldB} attribute
   */
  @Override
  public Date fieldB() {
    return fieldB;
  }

  /**
   * @return The value of the {@code fieldC} attribute
   */
  @Override
  public Long fieldC() {
    return fieldC;
  }

  /**
   * @return The value of the {@code fieldD} attribute
   */
  @Override
  public List fieldD() {
    return fieldD;
  }

  /**
   * Copy the current immutable object by setting a value for the {@link NewModel#fieldA() fieldA} attribute.
   * An equals check used to prevent copying of the same value by returning {@code this}.
   * @param value A new value for fieldA
   * @return A modified copy of the {@code this} object
   */
  public final ImmutableNewModel withFieldA(String value) {
    String newValue = Objects.requireNonNull(value, "fieldA");
    if (this.fieldA.equals(newValue)) return this;
    return new ImmutableNewModel(newValue, this.fieldB, this.fieldC, this.fieldD);
  }

  /**
   * Copy the current immutable object by setting a value for the {@link NewModel#fieldB() fieldB} attribute.
   * A shallow reference equality check is used to prevent copying of the same value by returning {@code this}.
   * @param value A new value for fieldB
   * @return A modified copy of the {@code this} object
   */
  public final ImmutableNewModel withFieldB(Date value) {
    if (this.fieldB == value) return this;
    Date newValue = Objects.requireNonNull(value, "fieldB");
    return new ImmutableNewModel(this.fieldA, newValue, this.fieldC, this.fieldD);
  }

  /**
   * Copy the current immutable object by setting a value for the {@link NewModel#fieldC() fieldC} attribute.
   * An equals check used to prevent copying of the same value by returning {@code this}.
   * @param value A new value for fieldC
   * @return A modified copy of the {@code this} object
   */
  public final ImmutableNewModel withFieldC(Long value) {
    Long newValue = Objects.requireNonNull(value, "fieldC");
    if (this.fieldC.equals(newValue)) return this;
    return new ImmutableNewModel(this.fieldA, this.fieldB, newValue, this.fieldD);
  }

  /**
   * Copy the current immutable object with elements that replace the content of {@link NewModel#fieldD() fieldD}.
   * @param elements The elements to set
   * @return A modified copy of {@code this} object
   */
  public final ImmutableNewModel withFieldD(String... elements) {
    List newValue = createUnmodifiableList(false, createSafeList(Arrays.asList(elements), true, false));
    return new ImmutableNewModel(this.fieldA, this.fieldB, this.fieldC, newValue);
  }

  /**
   * Copy the current immutable object with elements that replace the content of {@link NewModel#fieldD() fieldD}.
   * A shallow reference equality check is used to prevent copying of the same value by returning {@code this}.
   * @param elements An iterable of fieldD elements to set
   * @return A modified copy of {@code this} object
   */
  public final ImmutableNewModel withFieldD(Iterable elements) {
    if (this.fieldD == elements) return this;
    List newValue = createUnmodifiableList(false, createSafeList(elements, true, false));
    return new ImmutableNewModel(this.fieldA, this.fieldB, this.fieldC, newValue);
  }

  /**
   * This instance is equal to all instances of {@code ImmutableNewModel} that have equal attribute values.
   * @return {@code true} if {@code this} is equal to {@code another} instance
   */
  @Override
  public boolean equals(Object another) {
    if (this == another) return true;
    return another instanceof ImmutableNewModel
        && equalTo((ImmutableNewModel) another);
  }

  private boolean equalTo(ImmutableNewModel another) {
    return fieldA.equals(another.fieldA)
        && fieldB.equals(another.fieldB)
        && fieldC.equals(another.fieldC)
        && fieldD.equals(another.fieldD);
  }

  /**
   * Computes a hash code from attributes: {@code fieldA}, {@code fieldB}, {@code fieldC}, {@code fieldD}.
   * @return hashCode value
   */
  @Override
  public int hashCode() {
    int h = 5381;
    h += (h << 5) + fieldA.hashCode();
    h += (h << 5) + fieldB.hashCode();
    h += (h << 5) + fieldC.hashCode();
    h += (h << 5) + fieldD.hashCode();
    return h;
  }

  /**
   * Prints the immutable value {@code NewModel} with attribute values.
   * @return A string representation of the value
   */
  @Override
  public String toString() {
    return "NewModel{"
        + + fieldA
        + ", fieldB=" + fieldB
        + ", fieldC=" + fieldC
        + ", fieldD=" + fieldD
        + "}";
  }

  /**
   * Creates an immutable copy of a {@link NewModel} value.
   * Uses accessors to get values to initialize the new immutable instance.
   * If an instance is already immutable, it is returned as is.
   * @param instance The instance to copy
   * @return A copied immutable NewModel instance
   */
  public static ImmutableNewModel copyOf(NewModel instance) {
    if (instance instanceof ImmutableNewModel) {
      return (ImmutableNewModel) instance;
    }
    return ImmutableNewModel.builder()
        .from(instance)
        .build();
  }

  /**
   * Creates a builder for {@link ImmutableNewModel ImmutableNewModel}.
   * 
   * ImmutableNewModel.builder()
   *    .fieldA(String) // required {@link NewModel#fieldA() fieldA}
   *    .fieldB(Date) // required {@link NewModel#fieldB() fieldB}
   *    .fieldC(Long) // required {@link NewModel#fieldC() fieldC}
   *    .addFieldD|addAllFieldD(String) // {@link NewModel#fieldD() fieldD} elements
   *    .build();
   * 
   * @return A new ImmutableNewModel builder
   */
  public static ImmutableNewModel.Builder builder() {
    return new ImmutableNewModel.Builder();
  }

  /**
   * Builds instances of type {@link ImmutableNewModel ImmutableNewModel}.
   * Initialize attributes and then invoke the {@link #build()} method to create an
   * immutable instance.
   * 
{@code Builder} is not thread-safe and generally should not be stored in a field or collection,
   * but instead used immediately to create instances.
   */
  @Generated(from = "NewModel", generator = "Immutables")
  public static final class Builder {
    private static final long INIT_BIT_FIELD_A = 0x1L;
    private static final long INIT_BIT_FIELD_B = 0x2L;
    private static final long INIT_BIT_FIELD_C = 0x4L;
    private long initBits = 0x7L;

    private String fieldA;
    private Date fieldB;
    private Long fieldC;
    private List fieldD = new ArrayList();

    private Builder() {
    }

    /**
     * Fill a builder with attribute values from the provided {@code NewModel} instance.
     * Regular attribute values will be replaced with those from the given instance.
     * Absent optional values will not replace present values.
     * Collection elements and entries will be added, not replaced.
     * @param instance The instance from which to copy values
     * @return {@code this} builder for use in a chained invocation
     */
    public final Builder from(NewModel instance) {
      Objects.requireNonNull(instance, "instance");
      fieldA(instance.fieldA());
      fieldB(instance.fieldB());
      fieldC(instance.fieldC());
      addAllFieldD(instance.fieldD());
      return this;
    }

    /**
     * Initializes the value for the {@link NewModel#fieldA() fieldA} attribute.
     * @param fieldA The value for fieldA
     * @return {@code this} builder for use in a chained invocation
     */
    public final Builder fieldA(String fieldA) {
      this.fieldA = Objects.requireNonNull(fieldA, "fieldA");
      initBits &= ~INIT_BIT_FIELD_A;
      return this;
    }

    /**
     * Initializes the value for the {@link NewModel#fieldB() fieldB} attribute.
     * @param fieldB The value for fieldB
     * @return {@code this} builder for use in a chained invocation
     */
    public final Builder fieldB(Date fieldB) {
      this.fieldB = Objects.requireNonNull(fieldB, "fieldB");
      initBits &= ~INIT_BIT_FIELD_B;
      return this;
    }

    /**
     * Initializes the value for the {@link NewModel#fieldC() fieldC} attribute.
     * @param fieldC The value for fieldC
     * @return {@code this} builder for use in a chained invocation
     */
    public final Builder fieldC(Long fieldC) {
      this.fieldC = Objects.requireNonNull(fieldC, "fieldC");
      initBits &= ~INIT_BIT_FIELD_C;
      return this;
    }

    /**
     * Adds one element to {@link NewModel#fieldD() fieldD} list.
     * @param element A fieldD element
     * @return {@code this} builder for use in a chained invocation
     */
    public final Builder addFieldD(String element) {
      this.fieldD.add(Objects.requireNonNull(element, "fieldD element"));
      return this;
    }

    /**
     * Adds elements to {@link NewModel#fieldD() fieldD} list.
     * @param elements An array of fieldD elements
     * @return {@code this} builder for use in a chained invocation
     */
    public final Builder addFieldD(String... elements) {
      for (String element : elements) {
        this.fieldD.add(Objects.requireNonNull(element, "fieldD element"));
      }
      return this;
    }


    /**
     * Sets or replaces all elements for {@link NewModel#fieldD() fieldD} list.
     * @param elements An iterable of fieldD elements
     * @return {@code this} builder for use in a chained invocation
     */
    public final Builder fieldD(Iterable elements) {
      this.fieldD.clear();
      return addAllFieldD(elements);
    }

    /**
     * Adds elements to {@link NewModel#fieldD() fieldD} list.
     * @param elements An iterable of fieldD elements
     * @return {@code this} builder for use in a chained invocation
     */
    public final Builder addAllFieldD(Iterable elements) {
      for (String element : elements) {
        this.fieldD.add(Objects.requireNonNull(element, "fieldD element"));
      }
      return this;
    }

    /**
     * Builds a new {@link ImmutableNewModel ImmutableNewModel}.
     * @return An immutable instance of NewModel
     * @throws java.lang.IllegalStateException if any required attributes are missing
     */
    public ImmutableNewModel build() {
      if (initBits != 0) {
        throw new IllegalStateException(formatRequiredAttributesMessage());
      }
      return new ImmutableNewModel(fieldA, fieldB, fieldC, createUnmodifiableList(true, fieldD));
    }

    private String formatRequiredAttributesMessage() {
      List attributes = new ArrayList<>();
      if ((initBits & INIT_BIT_FIELD_A) != 0) attributes.add("fieldA");
      if ((initBits & INIT_BIT_FIELD_B) != 0) attributes.add("fieldB");
      if ((initBits & INIT_BIT_FIELD_C) != 0) attributes.add("fieldC");
      return "Cannot build NewModel, some of required attributes are not set " + attributes;
    }
  }

  private static  List createSafeList(Iterable iterable, boolean checkNulls, boolean skipNulls) {
    ArrayList list;
    if (iterable instanceof Collection) {
      int size = ((Collection) iterable).size();
      if (size == 0) return Collections.emptyList();
      list = new ArrayList<>();
    } else {
      list = new ArrayList<>();
    }
    for (T element : iterable) {
      if (skipNulls && element == null) continue;
      if (checkNulls) Objects.requireNonNull(element, "element");
      list.add(element);
    }
    return list;
  }

  private static  List createUnmodifiableList(boolean clone, List list) {
    switch(list.size()) {
    case 0: return Collections.emptyList();
    case 1: return Collections.singletonList(list.get(0));
    default:
      if (clone) {
        return Collections.unmodifiableList(new ArrayList<>(list));
      } else {
        if (list instanceof ArrayList) {
          ((ArrayList) list).trimToSize();
        }
        return Collections.unmodifiableList(list);
      }
    }
  }
}