Java基础之异常处理详解

try
{
   // 程序代码
}catch(ExceptionName e1)
{
   //Catch 块
}

// 文件名 : ExcepTest.java
import java.io.*;
public class ExcepTest{
 
   public static void main(String args[]){
      try{
         int a[] = new int[2];
         System.out.println("Access element three :" + a[3]);
      }catch(ArrayIndexOutOfBoundsException e){
         System.out.println("Exception thrown  :" + e);
      }
      System.out.println("Out of the block");
   }
}
// 以上代码编译运行输出结果如下：
// Exception thrown  :java.lang.ArrayIndexOutOfBoundsException: 3
// Out of the block

try{
   // 程序代码
}catch(异常类型1 异常的变量名1){
  // 程序代码
}catch(异常类型2 异常的变量名2){
  // 程序代码
}catch(异常类型3 异常的变量名3){
  // 程序代码
}

try {
    file = new FileInputStream(fileName);
    x = (byte) file.read();
} catch(FileNotFoundException f) { // Not valid!
    f.printStackTrace();
    return -1;
} catch(IOException i) {
    i.printStackTrace();
    return -1;
}

public void checkNumber(int num) {
  if (num < 0) {
    throw new IllegalArgumentException("Number must be positive");
  }
}

public void readFile(String filePath) throws IOException {
  BufferedReader reader = new BufferedReader(new FileReader(filePath));
  String line = reader.readLine();
  while (line != null) {
    System.out.println(line);
    line = reader.readLine();
  }
  reader.close();
}

import java.io.*;
public class className
{
   public void withdraw(double amount) throws RemoteException,
                              InsufficientFundsException
   {
       // Method implementation
   }
   //Remainder of class definition
}

try{
  // 程序代码
}catch(异常类型1 异常的变量名1){
  // 程序代码
}catch(异常类型2 异常的变量名2){
  // 程序代码
}finally{
  // 程序代码
}

public class ExcepTest{
  public static void main(String args[]){
    int a[] = new int[2];
    try{
       System.out.println("Access element three :" + a[3]);
    }catch(ArrayIndexOutOfBoundsException e){
       System.out.println("Exception thrown  :" + e);
    }
    finally{
       a[0] = 6;
       System.out.println("First element value: " +a[0]);
       System.out.println("The finally statement is executed");
    }
  }
}
// 实例编译运行结果如下：
// Exception thrown  :java.lang.ArrayIndexOutOfBoundsException: 3
// First element value: 6
// The finally statement is executed

// 语法中 try 用于声明和实例化资源，catch 用于处理关闭资源时可能引发的所有异常
try (resource declaration) {
  // 使用的资源
} catch (ExceptionType e1) {
  // 异常块
}

import java.io.*;

public class RunoobTest {

    public static void main(String[] args) {
        String line;
        try(BufferedReader br = new BufferedReader(new FileReader("test.txt"))) {
            while ((line = br.readLine()) != null) {
                System.out.println("Line =>"+line);
            }
        } catch (IOException e) {
            System.out.println("IOException in try block =>" + e.getMessage());
        }
    }
}
// 实例输出结果为：
// IOException in try block =>test.txt (No such file or directory)

import java.io.*;

class RunoobTest {
    public static void main(String[] args) {
        BufferedReader br = null;
        String line;

        try {
            System.out.println("Entering try block");
            br = new BufferedReader(new FileReader("test.txt"));
            while ((line = br.readLine()) != null) {
                System.out.println("Line =>"+line);
            }
        } catch (IOException e) {
            System.out.println("IOException in try block =>" + e.getMessage());
        } finally {
            System.out.println("Entering finally block");
            try {
                if (br != null) {
                    br.close();
                }
            } catch (IOException e) {
                System.out.println("IOException in finally block =>"+e.getMessage());
            }
        }
    }
}
// 实例输出结果为：
// Entering try block
// IOException in try block =>test.txt (No such file or directory)
// Entering finally block

import java.io.*;
import java.util.*;
class RunoobTest {
    public static void main(String[] args) throws IOException{
        try (Scanner scanner = new Scanner(new File("testRead.txt")); 
            PrintWriter writer = new PrintWriter(new File("testWrite.txt"))) {
            while (scanner.hasNext()) {
                writer.print(scanner.nextLine());
            }
        }
    }
}

class MyException extends Exception{
}

public class BankDemo {
    public static void main(String[] args) {
        // 创建账户类对象
        CheckingAccount c = new CheckingAccount(101);
        System.out.println("Depositing $500...");
        // 存钱
        c.deposit(500.00);
        try
        {
            //取钱
            System.out.println("\nWithdrawing $100...");
            c.withdraw(100.00);
            //取钱
            System.out.println("\nWithdrawing $600...");
            c.withdraw(600.00);
        }catch(InsufficientFundsException e)
        {
            //取钱异常，账户差额
            System.out.println("Sorry, but you are short $"
                    + e.getAmount());
            e.printStackTrace();
        }
    }
}


class InsufficientFundsException extends Exception
{
    //此处的amount用来储存当出现异常（取出钱多于余额时）所缺乏的钱
    private double amount;
    public InsufficientFundsException(double amount)
    {
        this.amount = amount;
    }
    public double getAmount()
    {
        return amount;
    }
}


class CheckingAccount
{
    //balance为余额，number为卡号
    private double balance;
    private int number;
    // 构造方法
    public CheckingAccount(int number)
    {
        this.number = number;
    }
    //方法：存钱
    public void deposit(double amount)
    {
        balance += amount;
    }
    //方法：取钱
    public void withdraw(double amount) throws
            InsufficientFundsException
    {
        if(amount <= balance)
        {
            balance -= amount;
        }
        else
        {
            double needs = amount - balance;
            throw new InsufficientFundsException(needs);
        }
    }
    //方法：返回余额
    public double getBalance()
    {
        return balance;
    }
    //方法：返回卡号
    public int getNumber()
    {
        return number;
    }
}
// 运行程序 BankDemo，得到结果如下所示：
// Depositing $500...

// Withdrawing $100...

// Withdrawing $600...
// Sorry, but you are short $200.0
// InsufficientFundsException
//	at CheckingAccount.withdraw(MammalInt.java:64)
//	at MammalInt.main(MammalInt.java:15)