为什么在catch里加上input = new Scanner(System.in);能够阻止无限循环

public static int inputCommand()

{

int a;

try

{

a = input.nextInt();

return a;

}catch(Exception e)

{

input = new Scanner(System.in);//阻止无限循环

//System.out.println("命令输入错误！请根据提示输入数字命令！");

return -1;

}

}