com.google.common.base

Class Objects

java.lang.Object

com.google.common.base.Objects

@GwtCompatible
public final class Objects
extends Object

Helper functions that can operate on any Object.

See the Guava User Guide on writing Object methods with Objects.

Since:

2.0 (imported from Google Collections Library)

Author:

Laurence Gonsalves

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	Objects.ToStringHelper Support class for toStringHelper(java.lang.Object).

Method Summary

Methods

Modifier and Type	Method and Description
static boolean	equal(Object a, Object b) Determines whether two possibly-null objects are equal.
static <T> T	firstNonNull(T first, T second) Returns the first of two given parameters that is not null, if either is, or otherwise throws a NullPointerException.
static int	hashCode(Object... objects) Generates a hash code for multiple values.
static Objects.ToStringHelper	toStringHelper(Class<?> clazz) Creates an instance of Objects.ToStringHelper in the same manner as toStringHelper(Object), but using the name of clazz instead of using an instance's Object.getClass().
static Objects.ToStringHelper	toStringHelper(Object self) Creates an instance of Objects.ToStringHelper.
static Objects.ToStringHelper	toStringHelper(String className) Creates an instance of Objects.ToStringHelper in the same manner as toStringHelper(Object), but using className instead of using an instance's Object.getClass().

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

equal

public static boolean equal(@Nullable
            Object a,
            @Nullable
            Object b)

Determines whether two possibly-null objects are equal. Returns:

• true if a and b are both null.
• true if a and b are both non-null and they are equal according to Object.equals(Object).
• false in all other situations.

This assumes that any non-null objects passed to this function conform to the equals() contract.

hashCode

public static int hashCode(@Nullable
           Object... objects)

Generates a hash code for multiple values. The hash code is generated by calling Arrays.hashCode(Object[]). Note that array arguments to this method, with the exception of a single Object array, do not get any special handling; their hash codes are based on identity and not contents.

This is useful for implementing Object.hashCode(). For example, in an object that has three properties, x, y, and z, one could write:

   public int hashCode() {
     return Objects.hashCode(getX(), getY(), getZ());
   }

Warning: When a single object is supplied, the returned hash code does not equal the hash code of that object.

toStringHelper

public static Objects.ToStringHelper toStringHelper(Object self)

Creates an instance of Objects.ToStringHelper.

This is helpful for implementing Object.toString(). Specification by example:

   // Returns "ClassName{}"
   Objects.toStringHelper(this)
       .toString();

   // Returns "ClassName{x=1}"
   Objects.toStringHelper(this)
       .add("x", 1)
       .toString();

   // Returns "MyObject{x=1}"
   Objects.toStringHelper("MyObject")
       .add("x", 1)
       .toString();

   // Returns "ClassName{x=1, y=foo}"
   Objects.toStringHelper(this)
       .add("x", 1)
       .add("y", "foo")
       .toString();

   // Returns "ClassName{x=1}"
   Objects.toStringHelper(this)
       .omitNullValues()
       .add("x", 1)
       .add("y", null)
       .toString();
   }

Note that in GWT, class names are often obfuscated.

Parameters:

self - the object to generate the string for (typically this), used only for its class name

Since:

2.0

toStringHelper

public static Objects.ToStringHelper toStringHelper(Class<?> clazz)

Creates an instance of Objects.ToStringHelper in the same manner as toStringHelper(Object), but using the name of clazz instead of using an instance's Object.getClass().

Note that in GWT, class names are often obfuscated.

Parameters:

clazz - the Class of the instance

Since:

7.0 (source-compatible since 2.0)

toStringHelper

public static Objects.ToStringHelper toStringHelper(String className)

Creates an instance of Objects.ToStringHelper in the same manner as toStringHelper(Object), but using className instead of using an instance's Object.getClass().

Parameters:

className - the name of the instance type

Since:

7.0 (source-compatible since 2.0)

firstNonNull

public static <T> T firstNonNull(@Nullable
                 T first,
                 @Nullable
                 T second)

Returns the first of two given parameters that is not null, if either is, or otherwise throws a NullPointerException.

Note: if first is represented as an Optional, this can be accomplished with first.or(second). That approach also allows for lazy evaluation of the fallback instance, using first.or(Supplier).

Returns:

first if first is not null, or second if first is null and second is not null

Throws:

NullPointerException - if both first and second were null

Since:

3.0