java.util.Objects, round two (original) (raw)

Joseph D. Darcy Joe.Darcy at Sun.COM
Tue Oct 13 23🔞13 UTC 2009

Hello.

After recent discussions on the list, the following methods will be included in round two of the evolution of java.util.Objects:

Under bug 6889858: Add nonNull methods to java.util.Objects:

/** * Checks that the specified object reference is not {@code null}. This * method is designed primarily for doing parameter validation in methods * and constructors, as demonstrated below: * 

     * public Foo(Bar bar) {
     *     this.bar = Objects.nonNull(bar);
     * }
     *
* * @param obj the object reference to check for nullity * @return {@code obj} if not {@code null} * @throws NullPointerException if {@code obj} is {@code null} */ public static T nonNull(T obj);

/**
 * Checks that the specified object reference is not {@code null} and
 * throws a customized {@link NullPointerException} if it is. This

method * is designed primarily for doing parameter validation in methods and * constructors with multiple parameters, as demonstrated below: * 

     * public Foo(Bar bar, Baz baz) {
     *     this.bar = Objects.nonNull(bar, "bar must not be null");
     *     this.baz = Objects.nonNull(baz, "baz must not be null");
     * }
     *
* * @param obj the object reference to check for nullity * @param message detail message to be used in the event that a {@code * NullPointerException} is thrown * @return {@code obj} if not {@code null} * @throws NullPointerException if {@code obj} is {@code null} */ public static T nonNull(T obj, String message);

Under bug 6891113: More methods for java.util.Objects: deepEquals, hash, toString with default /** * Returns {@code true} if the arguments are deeply equal to each other * and {@code false} otherwise. * * Two {@code null} values are deeply equal. If both arguments are * arrays, the algorithm in {@link Arrays.deepEquals(Object[], * Object[]) Arrays.deepEquals) is used to determine equality. * Otherwise, equality is determined by using the {@link Object#equals * equals} method of the first argument. * * @return {@code true} if the arguments are deeply equal to each other * and {@code false} otherwise * @see Arrays#deepEquals(Object[], Object[]) * @see Objects#equals(Object, Object) */ public static deepEquals(Object a, Object b);

/**
 * Returns the result of calling {@code toString} on the first
 * argument if the first argument is not {@code null} and returns
 * the second argument otherwise.
 *
 * @return the result of calling {@code toString} on the first
 * argument if it is not {@code null} and the second argument
 * otherwise.
 * @see Objects#toString(Object)
 */
public static toString(Object a, String nullDefault);

/**
 * Generates a hash code for a sequence of input values. The hash

code is * generated as if all the input values were placed into an array, and that * array were hashed by calling {@link Arrays#hashCode(Object[])}. * *

This method is useful for implementing {@link Object#hashCode()} on * objects containing multiple fields. For example, if an object that has * three fields, {@code x}, {@code y}, and {@code z}, one could write: * 

     * @Override public int hashCode() {
     *     return Objects.hashCode(x, y, z);
     * }
     *
* Warning: When a single object reference is supplied, the returned * value does not equal the hash code of that object reference. This * value can be computed by calling {@link #hashCode(Object)}. * * @return a hash value of the sequence of input values * @see Arrays#hashCode */ public static int hash(Object... components);

In addition, the Objects class will be explicitly marked as "final" to indicate its already implicit status as a non-instantiable, non-extendable class.

I've closed as "will not fix" the bug requesting to var-argify various constructors in String.

I'm open having being convinced that "toDefaultString(Object)" is a worthwhile addition to j.u.Objects as well.

Likewise, for "toDebugString(Object)", although someone else would have to specify, implement, and test that method.

-Joe

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