帮我检查一下这个JAVA程序哪里出错了

是用来计算个人所得税的，编译出现一大片的错误，我找了很久都找不出，麻烦各位帮忙看一下，在我的基础上看需要怎么改

import java.util.*;
public class Test4
{
double a,b,tax;
Scanner sc=new Scanner(System.in);
System.out.println("请输入本月工资:");
a=sc.nextDouble();
if(a<=1600)
System.out.println("不需缴纳税款");
else
b=a-1600;
if(b<=500)
tax=b*0.05;
else if(b<=2000)
tax=25+(b-500)*0.1;
else if(b<=5000)
tax=175+(b-2000)*0.15;
else if(b<=20000)
tax=625+(b-5000)*0.2;
else if(b<=40000)
tax=3625+(b-20000)*0.25;
else if(b<=60000)
tax=8625+(b-40000)*0.3;
else if(b<=80000)
tax=14625+(b-60000)*0.35;
else if(b<=100000)
tax=21625+(b-80000)*0.4;
else
tax=29625+(b-100000)*0.45;
System.out.println("个人所得税为:"+tax);
}

你没写进方法，你先写进main方法再编译。b也没初始化。编译出错的信息业贴上来

拿我改的试试

import java.util.*;
public class Test4
{
public static void main(String[] args)
{
double a,b = 0,tax;
Scanner sc=new Scanner(System.in);
System.out.println("请输入本月工资:");
a=sc.nextDouble();
if(a<=1600)
System.out.println("不需缴纳税款");
else
b=a-1600;
if(b<=500)
tax=b*0.05;
else if(b<=2000)
tax=25+(b-500)*0.1;
else if(b<=5000)
tax=175+(b-2000)*0.15;
else if(b<=20000)
tax=625+(b-5000)*0.2;
else if(b<=40000)
tax=3625+(b-20000)*0.25;
else if(b<=60000)
tax=8625+(b-40000)*0.3;
else if(b<=80000)
tax=14625+(b-60000)*0.35;
else if(b<=100000)
tax=21625+(b-80000)*0.4;
else
tax=29625+(b-100000)*0.45;
System.out.println("个人所得税为:"+tax);
}

}

你没把代码写进main方法