ObjectUtils.java

package com.kickstarter.libs.utils;

import android.support.annotation.NonNull;
import android.support.annotation.Nullable;

import rx.functions.Func1;

public final class ObjectUtils {
  private ObjectUtils(){}

  public static boolean isNull(final @Nullable Object object) {
    return object == null;
  }

  public static boolean isNotNull(final @Nullable Object object) {
    return object != null;
  }

  /**
   * Returns the first non-`null` value of its arguments.
   */
  @NonNull public static <T> T coalesce(final @Nullable T value, final @NonNull T theDefault) {
    if (value != null) {
      return value;
    }
    return theDefault;
  }

  /**
   * Returns a function `T -> T` that coalesces values with `theDefault`.
   */
  @NonNull public static <T> Func1<T, T> coalesceWith(final @NonNull T theDefault) {
    return (value) -> ObjectUtils.coalesce(value, theDefault);
  }

  /**
   * Converts a {@link String} to a {@link Boolean}, or null if the boolean cannot be parsed.
   */
  public static @Nullable Boolean toBoolean(final @Nullable String s) {
    if (s != null) {
      return Boolean.parseBoolean(s);
    }

    return null;
  }

  /**
   * Converts a {@link String} to an {@link Integer}, or null if the integer cannot be parsed.
   */
  public static @Nullable Integer toInteger(final @Nullable String s) {
    if (s != null) {
      try {
        return Integer.parseInt(s);
      } catch (final @NonNull NumberFormatException e) {
        return null;
      }
    }

    return null;
  }

  /**
   * Converts an {@link Integer} to a {@link String}, can be null if the integer is also null.
   */
  public static @Nullable String toString(final @Nullable Integer n) {
    if (n != null) {
      return Integer.toString(n);
    }

    return null;
  }

  /**
   * Converts a {@link Long} to a {@link String}, can be null if the long is also null.
   */
  public static @Nullable String toString(final @Nullable Long n) {
    if (n != null) {
      return Long.toString(n);
    }

    return null;
  }

  /**
   * Converts a {@link Float} to a {@link String}, can be null if the float is also null.
   */
  public static @Nullable String toString(final @Nullable Float n) {
    if (n != null) {
      return Float.toString(n);
    }

    return null;
  }

  /**
   * Converts a {@link Double} to a {@link String}, can be null if the double is also null.
   */
  public static @Nullable String toString(final @Nullable Double n) {
    if (n != null) {
      return Double.toString(n);
    }

    return null;
  }

  /**
   * Cast a `null`able value into a non-`null` value, and throw a `NullPointerException` if the value is `null`.
   */
  public static @NonNull <T> T requireNonNull(final @Nullable T value) throws NullPointerException {
    return requireNonNull(value, "Value should not be null.");
  }

  /**
   * Cast a `null`able value into a non-`null` value, and throw a `NullPointerException` if the value is `null`. Provide
   * a message for a better description of why you require this value to be non-`null`.
   */
  public static @NonNull <T> T requireNonNull(final @Nullable T value, final @NonNull Class<T> klass) throws NullPointerException {
    return requireNonNull(value, klass.toString() + " required to be non-null.");
  }

  /**
   * Cast a `null`able value into a non-`null` value, and throw a `NullPointerException` if the value is `null`. Provide
   * a message for a better description of why you require this value to be non-`null`.
   */
  public static @NonNull <T> T requireNonNull(final @Nullable T value, final @NonNull String message) throws NullPointerException {
    if (value == null) {
      throw new NullPointerException(message);
    }
    return value;
  }
}