在 Java 中，try、catch 和 finally 中的 return 是如何工作的?

2022-01-19 00:00:00 return try-catch java

我无法准确理解 return 在 try、catch 中的工作原理.

I can't understand exactly how return works in try, catch.

  • 如果我有 try 和 finally 而没有 catch，我可以将 return 放入 try 块.
  • 如果我有try、catch、finally，我不能把return放在尝试块.
  • 如果我有一个 catch 块，我必须将 return 放在 try、catch 之外，finally 块.
  • 如果我删除 catch 块和 throw Exception，我可以将 return 放在 try 块内.
  • If I have try and finally without catch, I can put return inside the try block.
  • If I have try, catch, finally, I can't put return in the try block.
  • If I have a catch block, I must put the return outside of the try, catch, finally blocks.
  • If I delete the catch block and throw Exception, I can put the return inside the try block.

它们究竟是如何工作的?为什么我不能将 return 放在 try 块中?

How do they work exactly? Why I can't put the return in the try block?

带有try、catch、finally

 public int insertUser(UserBean user) {
     int status = 0;

     Connection myConn = null;
     PreparedStatement myStmt = null;

     try {
         // Get database connection
         myConn = dataSource.getConnection();

         // Create SQL query for insert
         String sql = "INSERT INTO user "
                    + "(user_name, name, password) "
                    + "VALUES (?, ?, ?)";

         myStmt = myConn.prepareStatement(sql);

         // Set the parameter values for the student
         myStmt.setString(1, user.getUsername());
         myStmt.setString(2, user.getName());
         myStmt.setString(3, user.getPassword());

         // Execute SQL insert
         myStmt.execute();
     } catch (Exception exc) {
         System.out.println(exc);
     } finally {
         // Clean up JDBC objects
         close(myConn, myStmt, null);
     }

     return status;
 }

带有 try 的代码，finally 没有 catch

Code with try, finally without catch

 public int insertUser(UserBean user) throws Exception {
     int status = 0;

     Connection myConn = null;
     PreparedStatement myStmt = null;

     try {
         // Get database connection
         myConn = dataSource.getConnection();

         // Create SQL query for insert
         String sql = "INSERT INTO user "
                    + "(user_name, name, password) "
                    + "VALUES (?, ?, ?)";

         myStmt = myConn.prepareStatement(sql);

         // Set the parameter values for the student
         myStmt.setString(1, user.getUsername());
         myStmt.setString(2, user.getName());
         myStmt.setString(3, user.getPassword());

         // Execute SQL insert
         myStmt.execute();

         return status;
     } finally {
         // Clean up JDBC objects
         close(myConn, myStmt, null);
     }
 }

推荐答案

是的，很混乱.

在Java中，非void函数的所有程序控制路径必须以return结束，或抛出异常.这条规则说得很好，很简单.

In Java, all program control paths of a non-void function must finish with a return, or throw an exception. That's the rule put nice and simply.

但是，令人憎恶的是，Java 允许您将 extra return 放在 finally 块中，这会覆盖之前遇到的任何 返回:

But, in an abomination, Java allows you to put an extra return in a finally block, which overrides any previously encountered return:

try {
    return foo; // This is evaluated...
} finally {
    return bar; // ...and so is this one, and the previous `return` is discarded
}

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