Java 終止塊

Java 面向?qū)ο笤O(shè)計 - Java 終止塊

?try ?塊也可以有零個或一個? finally? 塊。 ?finally ?塊總是與 ?try ?塊一起使用。

語法

使用 ?finally? 塊的語法是

finally  {
    // Code for finally block 
}

?finally? 塊以關(guān)鍵字 ?finally? 開始，后面緊跟一對大括號。

?finally? 塊的代碼放在大括號內(nèi)。

?try?，?catch? 和? finally? 塊有兩種可能的組合:? try - catch - finally ?或? try - finally ?。

?try ?塊可以后跟零個或多個? catch? 塊。

?try? 塊最多可以有一個 ?finally? 塊。

?try? 塊必須有一個? catch? 塊，一個 ?finally? 塊，或者兩者兼而有之。

?try-catch-finally? 塊的語法是：

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

?try - finally ?塊的語法是：

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

無論在相關(guān)聯(lián)的? try ?和 ?/? 或 ?catch? 塊中發(fā)生什么，?finally ?塊都被保證被執(zhí)行。

通常，我們使用 ?finally? 塊來寫清理代碼。

例如，我們可能獲得一些資源，當(dāng)我們完成它們時，必須釋放。

?try - finally? 塊允許你實現(xiàn)這個邏輯。

您的代碼結(jié)構(gòu)將如下所示:

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

例子

下面的代碼演示了? finally ?塊的使用。

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.");
    }
  }
}

上面的代碼生成以下結(jié)果。

重新引用異常

捕獲的異?？梢灾匦乱谩?/p>

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);
  }
}

上面的代碼生成以下結(jié)果。