The data type boolean is incompatible for converting into any other data type. That is, a boolean value cannot be converted into any other data type like char, int, double etc. The maximum permitted is one boolean can be assigned to another boolean. Here, boolean to int is not permitted.
Following are not permitted.
boolean b = true;
int x = b; // error, boolean to int
int x = 10;
boolean y = x; // error, int to boolean
boolean b = true;
har ch = b; // error, boolean to char
char ch = 'A';
boolean b =ch; // error, char to boolean
Following is permitted (boolean assignment).
boolean b = true;
boolean b1 = b; // permitted
System.out.println(b1); // prints true
The keyword boolean is used in comparison operations.
int x = 10;
int y = 20;
boolean b = (x == y);
System.out.println(b); // prints false
Let us write a simple example to see the compiler message when boolean to int is casted.
public class Conversions
{
public static void main(String args[])
{
boolean b1 = true;
int i1 = b1; // error
System.out.println(b1);
}
}

Compiler message when boolean to int Java is done