Java 终止块

Java 面向对象设计 – Java 终止块

try ​块也可以有零个或一个​ finally​ 块。 ​finally ​块总是与 ​try ​块一起使用。

语法

使用 ​finally​ 块的语法是

finally  {
    // Code for finally block 
}

finally​ 块以关键字 ​finally​ 开始,后面紧跟一对大括号。

finally​ 块的代码放在大括号内。

try​,​catch​ 和​ finally​ 块有两种可能的组合:​ try - catch - finally ​或​ try - finally ​。

try ​块可以后跟零个或多个​ catch​ 块。

try​ 块最多可以有一个 ​finally​ 块。

try​ 块必须有一个​ catch​ 块,一个 ​finally​ 块,或者两者兼而有之。

try-catch-finally​ 块的语法是:

try  {
    // Code for try block
}
catch(Exception1 e1)  {
    // Code for catch block
}
finally  {
    // Code for finally block
}

try - finally ​块的语法是:

try  {
    // Code for try block
}
finally  {
    // Code for finally block
}

无论在相关联的​ try ​和 ​/​ 或 ​catch​ 块中发生什么,​finally ​块都被保证被执行。

通常,我们使用 ​finally​ 块来写清理代码。

例如,我们可能获得一些资源,当我们完成它们时,必须释放。

try - finally​ 块允许你实现这个逻辑。

您的代码结构将如下所示:

try  {
    // Obtain   and  use  some resources here
}
finally  {
    // Release the   resources that were  obtained in the   try  block
}

例子

下面的代码演示了​ finally ​块的使用。

public class Main {
  public static void main(String[] args) {
    int x = 10, y = 0, z = 0;
    try {
      System.out.println("Before dividing x by y.");
      z = x / y;
      System.out.println("After dividing x by y.");
    } catch (ArithmeticException e) {
      System.out.println("Inside catch block a.");
    } finally {
      System.out.println("Inside finally block a.");
    }

    try {
      System.out.println("Before setting z to 2.");
      z = 2;
      System.out.println("After setting z to 2.");
    }
    catch (Exception e) {
      System.out.println("Inside catch block b.");
    } finally {
      System.out.println("Inside finally block b.");
    }
    try {
      System.out.println("Inside try block c.");
    }
    finally {
      System.out.println("Inside finally block c.");
    }

    try {
      System.out.println("Before executing System.exit().");
      System.exit(0);
      System.out.println("After executing System.exit().");

    } finally {
      // This finally block will not be executed       // because application exits in try block       System.out.println("Inside finally block d.");
    }
  }
}

上面的代码生成以下结果。

重新引用异常

捕获的异常可以重新引用。

public class Main {
  public static void main(String[] args) {
    try {
      m1();
    } catch (MyException e) {
      // Print the stack trace       e.printStackTrace();
    }
  }

  public static void m1() throws MyException {
    try {
      m2();
    } catch (MyException e) {
      e.fillInStackTrace();
      throw e;
    }
  }

  public static void m2() throws MyException {
    throw new MyException("An error has occurred.");
  }
}

class MyException extends Exception {
  public MyException() {
    super();
  }

  public MyException(String message) {
    super(message);
  }

  public MyException(String message, Throwable cause) {
    super(message, cause);
  }

  public MyException(Throwable cause) {
    super(cause);
  }
}

上面的代码生成以下结果。

版权声明:本文采用知识共享 署名4.0国际许可协议 [BY-NC-SA] 进行授权
文章名称:《Java 终止块》
文章链接:https://zhuji.vsping.com/295265.html
本站资源仅供个人学习交流,请于下载后24小时内删除,不允许用于商业用途,否则法律问题自行承担。