null.equals("abc")    //   拋出 NullPointerException 異常
"abc".equals(null)    //   返回 false
null.equals(null)     //   拋出 NullPointerException 異常

Objects.equals(null, "abc")    //   返回 false
Objects.equals("abc",null)     //   返回 false
Objects.equals(null, null)     //   返回 true

"abc".equals("")    //  返回 false
"".equals("abc")    //  返回 false
"".equals("")       //  返回 true

public final class Objects {
    private Objects() {
        throw new AssertionError("No java.util.Objects instances for you!");
    }
 
    /**
     * Returns {@code true} if the arguments are equal to each other
     * and {@code false} otherwise.
     * Consequently, if both arguments are {@code null}, {@code true}
     * is returned and if exactly one argument is {@code null}, {@code
     * false} is returned.  Otherwise, equality is determined by using
     * the {@link Object#equals equals} method of the first
     * argument.
     *
     * @param a an object
     * @param b an object to be compared with {@code a} for equality
     * @return {@code true} if the arguments are equal to each other
     * and {@code false} otherwise
     * @see Object#equals(Object)
     */
    public static boolean equals(Object a, Object b) {
        return (a == b) || (a != null && a.equals(b));
    }

return (a == b) || (a != null && a.equals(b));