BAD OPTIMIZATION USING STRINGS

When there is a need to optimize the performance of Java code, the
suspicion usually falls on Strings. Although this is a good place to 
start,
sometimes developers overdo the optimization and create bad code.

It is a common mistake to think that if a String is constant, then it
should be changed to a static final variable to improve performance. 
This
is often accomplished with SQL statements.

public class Example {

static private final String SELECT_FROG =
"SELECT * FROM Frog where x=?";

.....
.....

public void doSomething(int x) {
...
...
Statement stmt = connection.
prepareStatement(SELECT_FROG);
stmt.setInt(x);
...
}

}

This overdone optimization quickly leads to a class in which all the 
SQL
statements have been converted to Java constants and the top of the
class. Each time a reader tries to understand the storage logic, the 
reader
has to flit backwards and forwards between doSomething and the 
SELECT_FROG
static attribute.

As is so often the case, the optimization leads to harder-to-read code.
And actually, the performance is not really enhanced. Java compilers 
are
perfectly able to handle the optimization of String literals. This even
works if the literal is split over lines with the + symbol. The correct
way to write the above code would be the far simpler and faster:

public class Example {

.....
.....

public void doSomething(int x) {
String sql = "SELECT * FROM
Frog where x=?";

...
...
Statement stmt = connection.
prepareStatement(sql);
stmt.setInt(x);
...
}

}

If the line of SQL is long, then it is perfectly fine, and in fact
desirable, to do:

String sql = "SELECT name,
place, age, id " +
" FROM
Record " +
" WHERE
name LIKE 'john' ";

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