循环

int i = 3;
while (i >= 0)
{
    System.out.println(i);
    i--;    //减 1
}

int i = 0;
while (i < 3)
{
    System.out.println(i);
    i++;   //加 1
}

boolean isExit = false;
while (!isExit)
{
    String s = buffer.readLine();
    isExit = s.equals("退出");
}

while (true) 
    System.out.println("C");

while (true) 
{
    String s = buffer.readLine();
    if (s.equals("退出")) 
        break;
}