为何会死循环

Question

int year=0,month=0,day=0,sum=0;

do{

System.out.println("请输入年");

if(input.hasNext()){

year=input.nextInt();

if(year>=1900){

}else{

System.out.println("错误！输入的年份不能小于1900年;\n请重新输入");

}while(true);

}

System.out.println("请输入月");

if(input.hasNext()){

month=input.nextInt();

if(month<=12||month>=1){

}else{

System.out.println("错误！你输入的月份有误；");

while(true);

}

}

System.out.println("请输入日");

if(input.hasNext()){

day=input.nextInt();

if(day<=31&day>=1){

if(day<=31&&month==1||month==3||month==5||month==7||month==8||month==10||month==12){

}else if(day<=30&&month==4||month==6||month==9||month==11){

}else if(month==2&&day<=29&&(year%4==0&&year%100!=0||year%400==0)){

}else if(month==2&&day<=28){

}else{

System.out.println("错误！"+year+"年的"+month+"月没有"+day+"天");

while(true);

}

}else{

System.out.println("错误！"+year+"年的"+month+"月没有"+day+"天");

while(true);

}

}

}while(true);

}

}