If it helps to wrap your mind around it, think of perl "strings" as java StringBuffers. For this perl code...

my  $output = "";
for (1 .. 1000) {
   $output .= get_long_string();
}
print $output;
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...the analogous java code is...

StringBuffer output = new StringBuffer();
for (1 .. 1000) {
   output.appends(get_long_string());
}
System.out.print(output.toString());
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I would not be surprised however if this perl code behaved as inefficiently as you might expect it to...

my  $output = "";
for (1 .. 1000) {
   $output = "" . get_long_string() . $output;
}
print $output;
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(but i haven't tested it ... perl might optimize it)