JDK7之java.util.Objects

JDK7开始引入的工具类

源码

package java.util;

import java.util.function.Supplier;

/**
 * @since 1.7
 */
public final class Objects {
    private Objects() {
        throw new AssertionError("No java.util.Objects instances for you!");
    }

   // 比较两个对象是否相等
    public static boolean equals(Object a, Object b) {
        return (a == b) || (a != null && a.equals(b));
    }

    public static boolean deepEquals(Object a, Object b) {
        if (a == b)
            return true;
        else if (a == null || b == null)
            return false;
        else
            return Arrays.deepEquals0(a, b);
    }

    /**
     * Returns the hash code of a non-{@code null} argument and 0 for
     * a {@code null} argument.
     */
    public static int hashCode(Object o) {
        return o != null ? o.hashCode() : 0;
    }

   /**
    * 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[])}.
    */
    public static int hash(Object... values) {
        return Arrays.hashCode(values);
    }

    /**
     * Returns the result of calling {@code toString} for a non-{@code
     * null} argument and {@code "null"} for a {@code null} argument.
     */
    public static String toString(Object o) {
        return String.valueOf(o);
    }

    /**
     * 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.
     */
    public static String toString(Object o, String nullDefault) {
        return (o != null) ? o.toString() : nullDefault;
    }

    /**
     * Returns 0 if the arguments are identical and {@code
     * c.compare(a, b)} otherwise.
     * Consequently, if both arguments are {@code null} 0
     * is returned.
     */
    public static <T> int compare(T a, T b, Comparator<? super T> c) {
        return (a == b) ? 0 :  c.compare(a, b);
    }

    /**
     * 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:
     * <blockquote><pre>
     * public Foo(Bar bar) {
     *     this.bar = Objects.requireNonNull(bar);
     * }
     * </pre></blockquote>
     */
    public static <T> T requireNonNull(T obj) {
        if (obj == null)
            throw new NullPointerException();
        return 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:
     * <blockquote><pre>
     * public Foo(Bar bar, Baz baz) {
     *     this.bar = Objects.requireNonNull(bar, "bar must not be null");
     *     this.baz = Objects.requireNonNull(baz, "baz must not be null");
     * }
     * </pre></blockquote>
     */
    public static <T> T requireNonNull(T obj, String message) {
        if (obj == null)
            throw new NullPointerException(message);
        return obj;
    }

    /**
     * Returns {@code true} if the provided reference is {@code null} otherwise
     * returns {@code false}.
     *
     * @see java.util.function.Predicate
     * @since 1.8
     */
    public static boolean isNull(Object obj) {
        return obj == null;
    }

    /**
     * Returns {@code true} if the provided reference is non-{@code null}
     * otherwise returns {@code false}.
     * @since 1.8
     */
    public static boolean nonNull(Object obj) {
        return obj != null;
    }

    /**
     * Checks that the specified object reference is not {@code null} and
     * throws a customized {@link NullPointerException} if it is.
     *
     * @since 1.8
     */
    public static <T> T requireNonNull(T obj, Supplier<String> messageSupplier) {
        if (obj == null)
            throw new NullPointerException(messageSupplier.get());
        return obj;
    }
}

引用

能够有效的避免空指针异常

@Test
public void testObjectsEquals() {
    Integer a = null;
    Integer b = 8;
    System.out.println("a==b " + Objects.equals(a, b));

    Integer c = 10;
    Integer d = null;
    System.out.println("c==d " + Objects.equals(c, d));

    Integer e = null;
    Integer f = null;
    System.out.println("e==f " + Objects.equals(e, f));

    Integer h = 12;
    Integer i = 15;
    System.out.println("h==i " + Objects.equals(h, i));

    Integer j = 25;
    Integer k = 25;
    System.out.println("j==k " + Objects.equals(j, k));

}

输出结果

a==b false
c==d false
e==f true
h==i false
j==k true

最后

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