带你全面认识Java中的异常处理

public static void main(String[] args) {
    // 数组索引越界异常: ArrayIndexOutOfBoundsException
    int[] arr = {10, 20, 40};
    System.out.println(arr[0]);
    System.out.println(arr[1]);
    System.out.println(arr[2]);
    System.out.println(arr[3]); // 越界

    // 异常提示: 
    // Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: Index 3 out of bounds for length 3
    //	at com.chenyq.d6_exception.ExceptionDemo.main(ExceptionDemo.java:11)
}

public static void main(String[] args) {
    String name = null;
    System.out.println(name.length()); // 空指针异常

    // 异常信息:
    // Exception in thread "main" java.lang.NullPointerException: Cannot invoke "String.length()" because "name" is null
    //	at com.chenyq.d6_exception.ExceptionDemo2.main(ExceptionDemo2.java:6)
}

public static void main(String[] args) {
    int c = 20 / 0; // 数学异常, 分母不能为0

    // 异常信息:
    // Exception in thread "main" java.lang.ArithmeticException: / by zero
    //	at com.chenyq.d6_exception.ExceptionDemo4.main(ExceptionDemo4.java:5)
}

public static void main(String[] args) {
        Object obj = 12;
    String str = (String) obj; // 类型转换异常

    // 异常信息
    // Exception in thread "main" java.lang.ClassCastException: class java.lang.Integer cannot be cast to class
    // java.lang.String (java.lang.Integer and java.lang.String are in module java.base of loader 'bootstrap')
    //	at com.chenyq.d6_exception.ExceptionDemo3.main(ExceptionDemo3.java:6
}

public static void main(String[] args) {
    String num1 = "23"; // 可以正常转换
    Integer res1 = Integer.valueOf(num1);
    System.out.println(res1 + 1);

    String num2 = "23aaa"; // 不可以正常转换 数字转换异常
    Integer res2 = Integer.valueOf(num2);
    System.out.println(res2 + 1);

    // 异常信息
    // Exception in thread "main" java.lang.NumberFormatException: For input string: "23aaa"
    //	at java.base/java.lang.NumberFormatException.forInputString(NumberFormatException.java:67)
    //	at java.base/java.lang.Integer.parseInt(Integer.java:668)
    //	at java.base/java.lang.Integer.valueOf(Integer.java:999)
    //	at com.chenyq.d6_exception.ExceptionDemo5.main(ExceptionDemo5.java:10)
}

public class winning {
    private static final String ID ="java";
    private static final String PassWord = "666";
    public static void main(String[] args) {
        System.out.println("请输入你的用户名");
        Scanner scanner=new Scanner(System.in);
        String name = scanner.nextLine();
        System.out.println("请输入你的密码");
        String password = scanner.nextLine();
    }
}

//定义一个用户名异常
class NameException extends RuntimeException{
    public NameException(String name){
        super(name);
    }
}

//定义一个密码异常
class PasswordException extends RuntimeException{
    public PasswordException(String password){
        super(password);
    }
}

public class winning {
    private static final String ID ="java";
    private static final String Password = "666";
    public static void main(String[] args) {
        System.out.println("请输入你的用户名");
        Scanner scanner=new Scanner(System.in);
        String name = scanner.nextLine();
        System.out.println("请输入你的密码");
        String password = scanner.nextLine();
        if (!ID.equals(name)){
            throw new NameException("用户名错了");
        }
        if (!Password.equals(password)){
            throw new PasswordException("密码有误");
        }
    }
}