while语句如何工作？

Question

I have an echo text Java code. I can't understand one of the statements? The code is:-

public class testing {

public static void main(String[] args) {
    boolean isRedirect = false;
    if(args.length != 0){
        isRedirect = true;
    }
    int ch;
    try{
        while ((ch = System.in.read()) != ((isRedirect) ? -1 : '\n'))
        System.out.print((char) ch);
    }
    catch(java.io.IOException ioe){
        System.err.println("I/O Error");
    }
    System.out.println();
}
}

I know the code creates a Boolean to check whether the input is coming or not. I know the while loop is outputting integers that '(char)' is converting to characters but I don't understand how the while statement does this. Thanks in advance.

Answer 1

while ((ch = System.in.read()) != ((isRedirect) ? -1 : '\n'))

has the same effect as:

do {
    ch = System.in.read();
} while(ch != (isRedirect ? -1 : '\n'));

which has the same effect as:

if(isRedirect) {
    do {
        ch = System.in.read();
    } while(ch != -1);

} else {

    do {
        ch = System.in.read();
    } while(ch != '\n');
}

which is hopefully understandable.