java自定义异常以及throw和throws关键字用法

public class MyException extends Exception{ //创建自定义异常
public MyException(String ErrorExceptin){ //构造方法
 super(ErrorExceptin); //父类构造方法
}
}

public class TestException {
//定义方法，抛出异常
private static int Sum(int num1,int num2)throws MyException{
 if(num1<0||num2<0){ //判断方法中参数是否满足条件
 throw new MyException("输入参数为负数"); //错误信息
 }
 if(num1>20||num2>20){ //判断方法中参数是否满足条件
 throw new MyException("输入参数大于20");//错误信息
 }
 return (num1+num2); //将两个数的和输出
}
public static void main(String []args){
 try {  //try代码块处理可能出现的异常
 int result=Sum(22,23); //调用Sum()方法
 System.out.println(result); //将Sum()方法的返回值输出
 } catch (MyException e) { 
 // TODO: handle exception
 System.out.println(e); //输出异常信息
 }
}
}

public class NullpointExceptionTest {
static void testNull()throws NullPointerException{
 String s = null;
 if(s==null){
 throw new NullPointerException();
 }
}
public static void main(String []args){
 try {
 testNull();
 } catch (NullPointerException e) {
 // TODO: handle exception
 System.out.println("testNull()中抛出的异常是"+e);
 }
}
}

//如果是继承Exception，则在手动抛出的是时候显示处理，或者丢给jvm
class MyException extends RuntimeException {
 //序列号
 static final long serialVersionUID = -70348971102145766939L;
 public MyException() {
 
 }
 public MyException(String msg) {
 super(msg);
 }
}
public class TestException4 {
 public static void main(String[] args) {
 Student s = new Student();
 s.register(-1);
 //自定义异常类，try-catch-finally中的使用
 try {
 s.register(-11);
 } catch (MyException e) {
 System.out.println(e.getMessage());
 }
 System.out.println(s);
 }
}
class Student{
 int id;
 public void register(int id) {
 if(id>0) {
 this.id = id;
 }else {
 //手动抛出一个异常的使用
 throw new MyException("传入的id有误");
 }
 }
 @Override
 public String toString() {
 return "Student [id=" + id + "]";
 }
 
}