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From: =?UTF-8?Q?Arne_Vajh=c3=b8j?= <arne@vajhoej.dk>
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Subject: Re: Testing the functionality of sub classes
Date: Sun, 20 Aug 2017 13:06:46 -0400
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On 8/20/2017 12:28 PM, Arne Vajhøj wrote:
> On 8/20/2017 12:13 PM, Cecil Westerhof wrote:
>> Arne Vajhøj <arne@vajhoej.dk> writes:
>>>> Nope, it shows that the H2 driver does follow the standards (and the
>>>> SQLite3 driver does not). The first ResultSet is closed as it should
>>>> be. You can do an isClosed on it. So it is not null, but displays a
>>>> null to show you should not use it anymore.
>>>
>>> The contract for toString is extremely vague.
>>>
>>> I do not see any indication than SQLite does not follow
>>> JDBC standard.
>>>
>>> Reusing result set object should be perfectly valid
>>> per JDBC standard.
>>
>> In the description of Statement (copied with spelling mistakes):
>>      All execution methods in the Statement interface implicitly close
>>      a statment's current ResultSet object if an open one exists.
> 
> It is exactly because of this that I think reuse is valid.

Maybe I am just babbling.

But let me try and show what I am thinking about.

The code is far from complete, but it should hopefully
illustrate what I am thinking about.

public class OpenCloseFun {
	public static interface Connection extends AutoCloseable {
		public Statement createStatement();
	}
	public static interface Statement extends AutoCloseable {
		public ResultSet executeQuery(String sql);
	}
	public static interface ResultSet extends AutoCloseable {
		public boolean next();
	}
	public static class MyConnection implements Connection {
		private MyRealConnection real;
		private MyConnection(MyRealConnection real) {
			this.real = real;
		}
		public static MyConnection create() {
			return new MyConnection(new MyRealConnection());
		}
		public Statement createStatement() {
			return new MyStatement(real.createStatement());
		}
		public void close() throws Exception {
			real.close();
		}
		public String toString() {
			return real.toString();
		}
	}
	public static class MyStatement implements Statement {
		private MyRealStatement real;
		public MyStatement(MyRealStatement real) {
			this.real = real;
		}
		public ResultSet executeQuery(String sql) {
			return new MyResultSet(real.executeQuery(sql));
		}
		public void close() throws Exception {
			real.close();
		}
		public String toString() {
			return real.toString();
		}
	}
	public static class MyResultSet implements ResultSet {
		private MyRealResultSet real;
		public MyResultSet(MyRealResultSet real) {
			this.real = real;
		}
		public boolean next() {
			return real.next();
		}
		public void close() throws Exception {
			real.close();
		}
		public String toString() {
			return real.toString();
		}
	}
	public static class MyRealConnection implements Connection {
		private MyRealStatement stmt = new MyRealStatement(); // only one 
concurrent active Statement per Connection
		public MyRealStatement createStatement() {
			stmt.init();
			return stmt;
		}
		public void close() throws Exception {
			stmt.close();
		}
	}
	public static class MyRealStatement implements Statement {
		private MyRealResultSet rs = new MyRealResultSet(); // only one 
concurrent active ResultSet per Statement
		public void init() {
		}
		public MyRealResultSet executeQuery(String sql) {
			rs.init(sql);
			return rs;
		}
		public void close() throws Exception {
			rs.close();
		}
	}
	public static class MyRealResultSet implements ResultSet {
		public void init(String sql) {
		}
		public boolean next() {
			return true;
		}
		public void close() throws Exception {
		}
	}
	public static void main(String[] args) throws Exception {
		try(Connection con = MyConnection.create()) {
			try(Statement stmt = con.createStatement();
			    ResultSet rs1 = stmt.executeQuery("something");
				ResultSet rs2 = stmt.executeQuery("something else")) {
				System.out.println(stmt);
				System.out.println(rs1);
				System.out.println(rs2);
			}
		}
	}
}

Arne