While code, Method, Int to boolean understanding

I'm reviewing some code for a college assignment and we've been given examples to assist us.
I'm little confused on what the below is doing as it's using the assignment operator instead of the .equals or == method.

If I replace the code with the == (and create a local variable to compare it to) the code starts infinite looping and displaying out the default value.

 int select = 0;
 
  do {
    
        switch (select) {
            case 1:
                Problem();
                break; 
            default:
            System.out.println("Invalid");
            break;
            } 

    } while ((select = getSelection()) !=3);

 public static int getSelection () { 
(Return function here with has.nextInt and scanner class to receive input)
}

From my limited understanding, the above assigns "Select" to the value from the "getSelection" method, it's also stating do not accept inputs that are 3 e.g. System.exit0 at this point.

Have I understood correctly?

(Further example as requested)
I would do something along the lines of:

int select = 0; 
int select1 = 0; 
    do {

    switch (select) {
        case 1:
            Problem();
            break; 
        default:
        System.out.println("Invalid");
        break;
        } 
 } while (select == select1);

I am attempting to think of a logical equivalent to the lecturers example but seem to be unable to do this without breaking the while loop.

In java, (and other "C like" languages) the result of an assignment is the value assigned, ie this code:

do {
    // other code
} while ((select = getSelection()) !=3)

is the same as:

do {
    // other code
    select = getSelection();
} while (select != 3)

This style, known as in-line conditional, is generally considered a style to be avoided.

There is a checkstyle violation for it - see AvoidInlineConditionals