## 1.概述

In this tutorial, we’ll look at some ways to check whether an integer exists within a given range. We’ll do that using operators as well as several utility classes.

## 2.射程类型

Before we use any of these methods, we have to be clear about what kind of range we’re talking about. We’ll focus on these four bounded range types throughout this tutorial:

• closed rangeincludes its lower and upper bounds
• open rangeexcludes its lower and upper bounds
• left-open right-closed rangeincludes its upper bound and excludes it’s lower bound
• left-closed right-open range includes its lower bound and excludes it’s upper bound

For example, suppose we wanted to know whether the integer 20 occurs within these two ranges: R1 = [10, 2o), a left-closed right-open range, and R2 = (10, 20], a left-open right-closed range. Since R1 does not contain its upper bound, the integer 20 exists only in R2.

## 3.使用<和<=操作符

Our goal is to determine whether a number is between a given lower and upper bound. We’ll start by checking for this using basic Java operators.

Let’s define a class that does this check for all four kinds of ranges:

``````public class IntRangeOperators {

public static boolean isInClosedRange(Integer number, Integer lowerBound, Integer upperBound) {
return (lowerBound <= number && number <= upperBound);
}

public static boolean isInOpenRange(Integer number, Integer lowerBound, Integer upperBound) {
return (lowerBound < number && number < upperBound);
}

public static boolean isInOpenClosedRange(Integer number, Integer lowerBound, Integer upperBound) {
return (lowerBound < number && number <= upperBound);
}

public static boolean isInClosedOpenRange(Integer number, Integer lowerBound, Integer upperBound) {
return (lowerBound <= number && number < upperBound);
}
}``````

Here, by changing the operators to include or exclude the bounds, we can tune the interval to be open, closed, or half-open.

Let’s test our static isInOpenClosedRange() method. We’ll specify the left-open right-closed range (10,20] by passing in 10 for the lower bound and 20 for the upper bound:

``````assertTrue(IntRangeClassic.isInOpenClosedRange(20, 10, 20));

assertFalse(IntRangeClassic.isInOpenClosedRange(10, 10, 20));``````

In our first test, we successfully verified that the integer 20 exists in the (10,20] range, which includes its upper bound. We then confirmed that the integer 10 does not exist in the same range, which excludes its lower bound.

## 4.使用范围类

As an alternative to using Java operators, we can also use utility classes that represent ranges. The primary benefit to using pre-defined classes is that range classes offer out-of-the-box implementations for some or all the range types described above.

Additionally, we can configure a range object with our defined bounds and reuse the object in other methods or classes. By defining the range once, our code is less error-prone if we need to do multiple checks against the same range throughout our code base.

On the other hand, two of the range classes we’ll look at below are in external libraries that must be imported into our project before we can use them.

### 4.1.使用java.time.temporal.ValueRange。

A range class that does not require importing an external library is java.time.temporal.ValueRange, introduced in JDK 1.8:

``````public class IntRangeValueRange {

public boolean isInClosedRange(Integer number, Integer lowerBound, Integer upperBound) {
final ValueRange range = ValueRange.of(lowerBound, upperBound);
return range.isValidIntValue(number);
}

public boolean isInOpenRange(Integer number, Integer lowerBound, Integer upperBound) {
final ValueRange range = ValueRange.of(lowerBound + 1, upperBound - 1);
return range.isValidIntValue(number);
}

public boolean isInOpenClosedRange(Integer number, Integer lowerBound, Integer upperBound) {
final ValueRange range = ValueRange.of(lowerBound + 1, upperBound);
return range.isValidIntValue(number);
}

public boolean isInClosedOpenRange(Integer number, Integer lowerBound, Integer upperBound) {
final ValueRange range = ValueRange.of(lowerBound, upperBound - 1);
return range.isValidIntValue(number);
}
}
``````

As we can see above, we created ValueRange objects by passing lowerBound and upperBound to the static of() method. We then checked whether number existed within each range by using each object’s isValidIntValue() method.

We should note that ValueRange only supports closed range checks out of the box. Because of that, we must validate left-open ranges by incrementing lowerBound, and right-open ranges by decrementing upperBound, as we do above.

### 4.2.使用Apache Commons

Let’s move on to some range classes we can use from third-party libraries. First, we’ll add the Apache Commons dependency to our project:

``````<dependency>
<groupId>org.apache.commons</groupId>
<artifactId>commons-lang3</artifactId>
<version>3.12.0</version>
</dependency>``````

Here, we’re implementing the same behavior as before, but using the Apache Commons Range class:

``````public class IntRangeApacheCommons {

public boolean isInClosedRange(Integer number, Integer lowerBound, Integer upperBound) {
final Range<Integer> range = Range.between(lowerBound, upperBound);
return range.contains(number);
}

public boolean isInOpenRange(Integer number, Integer lowerBound, Integer upperBound) {
final Range<Integer> range = Range.between(lowerBound + 1, upperBound - 1);
return range.contains(number);
}

public boolean isInOpenClosedRange(Integer number, Integer lowerBound, Integer upperBound) {
final Range<Integer> range = Range.between(lowerBound + 1, upperBound);
return range.contains(number);
}

public boolean isInClosedOpenRange(Integer number, Integer lowerBound, Integer upperBound) {
final Range<Integer> range = Range.between(lowerBound, upperBound - 1);
return range.contains(number);
}
}``````

As with ValueRange‘s of() method, we passed lowerBound and upperBound to Range‘s static between() method to create Range objects. We then used the contains() method to check whether number existed within each object’s range.

ValueRangeof()方法一样，我们将lowerBoundupperBound传递给Rangestatic between()方法以创建Range对象。然后我们使用contains()方法来检查number是否存在于每个对象的范围内。

The Apache Commons Range class also only supports closed intervals, but we simply adjusted lowerBound and upperBound again as we did with ValueRange.

Apache Commons的Range类也只支持封闭的区间，但我们只是像对待ValueRange那样再次调整lowerBoundupperBound

Moreover, as a generic class, Range can be used not only for Integer but for any other type that implements Comparable.

``````<dependency>
<artifactId>guava</artifactId>
<version>31.1-jre</version>
</dependency>``````

We can use Guava’s Range class to reimplement the same behavior as before:

``````public class IntRangeGoogleGuava {

public boolean isInClosedRange(Integer number, Integer lowerBound, Integer upperBound) {
final Range<Integer> range = Range.closed(lowerBound, upperBound);
return range.contains(number);
}

public boolean isInOpenRange(Integer number, Integer lowerBound, Integer upperBound) {
final Range<Integer> range = Range.open(lowerBound, upperBound);
return range.contains(number);
}

public boolean isInOpenClosedRange(Integer number, Integer lowerBound, Integer upperBound) {
final Range<Integer> range = Range.openClosed(lowerBound, upperBound);
return range.contains(number);
}

public boolean isInClosedOpenRange(Integer number, Integer lowerBound, Integer upperBound) {
final Range<Integer> range = Range.closedOpen(lowerBound, upperBound);
return range.contains(number);
}
}``````

We can see above that Guava’s Range class has four separate methods for creating each range type we discussed earlier. That is, unlike the other range classes we’ve seen so far, Guava’s Range class natively supports open and half-open ranges. For example, to specify a half-open interval that excludes its upper bound, we passed lowerBound and upperBound to the static closedOpen() method. For a half-open interval that excludes its lower bound, we used openClosed(). We then checked whether number existed in each range using the contains() method.

## 5.总结

In this article, we learned how to use basic operators and range classes to check whether an integer falls within a given range. We also explored the pros and cons of the various approaches.

As always, the source code for these examples is available over on GitHub.