Java – Find Arc Cosine – acos() Method – Examples & Explanation

acos() method exists in Math class of java.lang package.
Since: JDK1.0

The declaration of acos() method is:

public static double acos(double x)

The syntax of acos() method in Java is:

 
java.lang.Math.acos(double x)

Example

/*
*Find the arc cosine of given input(double) without importing the 
java.lang Package.
*/
public class JavaMathExample {
    public static void main(String[] args) {
        //Declaring variables
        double x = 0.5;
        double result;
        //Assign arc cosine of x to result variable
        result = java.lang.Math.acos(x);
        //Printing result to the console
        System.out.println(result);
    }
}

Output:

1.0471975511965979

Example
By importing java.lang package the syntax of acos() method can be used as:

/*
*Find the inverse of cosine or arc cosine of given input(double) by importing the java.lang Package.
*/
import java.lang.*;  //importing package

public class JavaMathExample {
    public static void main(String[] args) {
        
        //Declaring variables
        double x = 0.5;
        double result;
        
        //Assign arc cosine of x to result variable
        result = Math.acos(x);
        
        //Printing result to the console
        System.out.println(result);
    }
}

Output:

1.0471975511965979


x – Where x is any valid double input value. This parameter is required.

If the x parameter is not a number acos() method returns an error.
If there is no argument (x – input value) passes to the method, the compiler will produce an error.
Example

/*
*This example returns a compile time error
*/
import java.lang.*; //importing java.lang package

public class JavaMathExample {
    public static void main(String[] args) {

        //Declaring variables
        String x = "Not a number";
        double result;

        //argument is not a number
        result = Math.acos(x);
        System.out.println(result);

        //Here no argument is used
        result = Math.acos();
        System.out.println(result);


    }

}

Output:
Error

acos() method returns the arc cosine of a double value for the given input (x – parameter).

import java.lang.*; //importing java.lang package

public class JavaMathExample {
    public static void main(String[] args) {
        double negativeValue = -18.869;
        double positiveValue = 27.78639;
        double zero = 0;
        System.out.println("arc cosine of a Negative Value: "+Math.acos(negativeValue));
        System.out.println("arc cosine of a Positive Value: "+Math.acos(positiveValue));
        System.out.println("arc cosine of Zero: "+Math.acos(zero));

    }
}

Output:

arc cosine of a Negative Value: 2.0943951023931957
arc cosine of a Positive Value: 1.0471975511965979
arc cosine of Zero: 1.5707963267948966


import java.lang.*; //importing java.lang package

public class JavaMathExample {
    public static void main(String[] args) {
        //Declare and initialize an array containing double values
        double test [] = { Double.MAX_VALUE, Double.MIN_VALUE, 
		Double.NaN, Double.MIN_EXPONENT, 42.867e-12, 16.852, 0, -2.58, -78.8569e7 };

        //Use for loop to print arc cosine of each element of the array
        for (int i=0; i < test.length; i++) {
            System.out.println(  Math.acos(test[i])  );
        }

    }
}

Output:

NaN
1.5707963267948966
NaN
NaN
1.5707963267520295
NaN
1.5707963267948966
NaN
NaN

NOte : Those values which are not in the range of (0.0 through Pi) will return a NaN value.

If the argument is NaN or its absolute value is greater than 1, then the result is NaN.
Example

/*
*This example shows some special cases of acos() method in Java
*/
import java.lang.*; //importing java.lang package

public class JavaMathExample {
    public static void main(String[] args) {

        //Declaring variables

       
        double nan = Double.NaN;
        double result;

        //Here argument is NaN, output will be NaN
        result = Math.acos(nan);
        System.out.println(result);


    }

}

Output:

NaN