Check if a variable is between two numbers with Java

//If "x" is between "a" and "b";

.....

int m = (a+b)/2;

if(Math.abs(x-m) <= (Math.abs(a-m)))

{
(operations)
}

......

//have to use floating point conversions if the summ is not even;

Simple example :

//if x is between 10 and 20

if(Math.abs(x-15)<=5)

public static boolean between(int variable, int minValueInclusive, int maxValueInclusive) {
    return variable >= minValueInclusive && variable <= maxValueInclusive;
}

A Java method to determine if an integer is between a range

You can use apache Range API. https://commons.apache.org/proper/commons-lang/apidocs/org/apache/commons/lang3/Range.html

I see some errors in your code.
Your probably meant the mathematical term

90 <= angle <= 180, meaning angle in range 90-180.

if (angle >= 90 && angle <= 180) {

// do action
}