Ordering is Guava’s fluent Comparator class and implements Comparator interface. It can be used to build complex comparators and apply them to collections of objects.

Okay, so let’s getting started. Firstly, we declared a String type List:

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private List<String> locations = Lists.newArrayList(
        "Guang zhou",
        "Cheng du",
        "",
        "Shang hai"
);

We will use this locations variable later.

Usage

Objects.equal(Object, Object)
Invoking this method then it will avoid the risking of NullPointerException when we need to compare two object whether they equal.

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Objects.equal("a", "a"); // return true;
Objects.equal(null, "a"); // return false;
Objects.equal(null, null); // return true;

Guava provides a number of precondition checking utilities. It’s Preconditions class. You can use it into your project.

Usage

checkArgument(boolean)
Checks that the boolean is true. Use for validating arguments to methods.

checkNotNull(T)
Checks that the value is not null. Returns the value directly, so you can use checkNotNull(value) inline.

Optional<T> is a way of replacing a nullable T reference with a non-null value. An Optional may either contain a non-null T reference (in which case we say the reference is “present”), or it may contain nothing (in which case we say the reference is “absent”). It is never said to “contain null.”