**1. Introduction**

In this short tutorial, we'll look at how to calculate sine values using Java's *Math.sin()* function and how to convert angle values between degrees and radians.

**2. Radians vs. Degrees**

By default, the** Java ***Math* library expects values to its trigonometric functions to be in radians.

As a reminder, *radians *are just another way to express the measure of an angle, and the conversion is:

```
double inRadians = inDegrees * PI / 180;
inDegrees = inRadians * 180 / PI;
```

Java makes this easy with *toRadians *and *toDegrees*:

```
double inRadians = Math.toRadians(inDegrees);
double inDegrees = Math.toDegrees(inRadians);
```

Whenever we are using any of Java's trigonometric functions, **we should first think about what is the unit of our input**.

**3. Using ***Math.sin*

We can see this principle in action by taking a look at the *Math.s**in* method, one of the many that Java provides:

`public static double sin(double a)`

It's equivalent to the mathematical sine function and **it expects its input to be in radians**. So, let's say that we have an angle we know to be in degrees:

`double inDegrees = 30;`

We first need to convert it to radians:

`double inRadians = Math.toRadians(inDegrees);`

And then we can calculate the sine value:

`double sine = Math.sin(inRadians);`

But,** if we know it to already be in radians, then we don't need to do the conversion**:

```
@Test
public void givenAnAngleInDegrees_whenUsingToRadians_thenResultIsInRadians() {
double angleInDegrees = 30;
double sinForDegrees = Math.sin(Math.toRadians(angleInDegrees)); // 0.5
double thirtyDegreesInRadians = 1/6 * Math.PI;
double sinForRadians = Math.sin(thirtyDegreesInRadians); // 0.5
assertTrue(sinForDegrees == sinForRadians);
}
```

Since *thirtyDegreesInRadians *was already in radians, we didn't need to first convert it to get the same result.

**4. Conclusion**

In this quick article, we've reviewed radians and degrees and then saw an example of how to work with them using *Math.sin.*

As always, check out the source code for this example over on GitHub.

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