一篇文章带你深入了解Java异常

System.out.println(10/0);
// 执行结果
Exceptioninthread"main"java.lang.ArithmeticException: /byzero

int[] arr= {1, 2, 3};
System.out.println(arr[100]);
// 执行结果
Exceptioninthread"main"java.lang.ArrayIndexOutOfBoundsException: 100

publicclassTest {
    publicintnum=10;
    publicstaticvoidmain(String[] args) {
        Testt=null;
        System.out.println(t.num);
    }
}
// 执行结果
Exceptioninthread"main"java.lang.NullPointerException

try{    
有可能出现异常的语句 ; 
}[catch (异常类型异常对象) {} ... ]
[finally {
异常的出口}]

int[] arr= {1, 2, 3};
try {
    System.out.println("before");
    System.out.println(arr[100]);
    System.out.println("after");
} catch (ArrayIndexOutOfBoundsExceptione) {    // 打印出现异常的调用栈
    e.printStackTrace();
}
System.out.println("after try catch");
// 执行结果
before
java.lang.ArrayIndexOutOfBoundsException: 100
atdemo02.Test.main(Test.java:10)aftertrycatch

int[] arr= {1, 2, 3};
try {
    System.out.println("before");
    arr=null;
    System.out.println(arr[100]);
    System.out.println("after");
} catch (Exceptione) {
    e.printStackTrace();
} finally {
    System.out.println("finally code");}
// 执行结果
before
java.lang.NullPointerException
atdemo02.Test.main(Test.java:12)finallycode

publicstaticintfunc() {    try {
        return10;
    } finally {
        return20;
    }
}

publicstaticintdivide(intx, inty) {
    if (y==0) {
        thrownewArithmeticException("抛出除 0 异常");    }
    returnx/y;
}

public static void main(String[] args) {
    try {
        login("admin", "123456");
    } catch (UserError userError) {
        userError.printStackTrace();
    } catch (PasswordError passwordError) {        
    passwordError.printStackTrace();
    }
}
public static void login(StringuserName, Stringpassword) throwsUserError,  PasswordError {
    if (!Test.userName.equals(userName)) {
        throw new UserError("用户名错误");
    }
    if (!Test.password.equals(password)) {
        throw new PasswordError("密码错误");
    }
    System.out.println("登陆成功");
}
class UserError extends Exception {
    publicUserError(Stringmessage) {        
    super(message);
    }
}
class PasswordError extends Exception {
    public PasswordError(Stringmessage) {        
    super(message);
    }
}