How to resolve the "java illegal start of expression" error

$1.$ Missing an opening or closing curly bracket for a code block (i.e., function, conditional code, loop, etc):

public void foo(){
    System.out.println("No closing bracket for this function.");

This has to be resolved manually by looking for a pair of curly brackets for each code block and completing the missing ones.

$2.$ Declaring a function inside another function:

public void foo(){
    // Declaring bar() inside foo():
    private int bar(){
        return 10;
    }
}

Move the function declared inside (i.e., bar()) to an appropriate place outside the outer function (i.e., foo()).

$3.$ Using an access specifier with a function's local variable:

private int foo(){
    // Writing 'public' with 'int':
    public int x = 5;
    return x;
}

The local variables of a function are only visible inside it and their scope cannot be widened or narrowed. Remove the access specifiers of the variables to resolve this error.