ORA-01722

Please advice why I have ORA-01722 if local variable is double

double[] outY = new double[10];

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sql

System.out.println(outY[0] + "  = outY[0]  "  + new java.util.Date());
sql_Y = " INSERT INTO RBF_DATA " + "(OUTY0) " + "VALUES " + "('" + outY[0] + "')";

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and output

0.12258723414643523  = outY[0]  Fri Feb 11 19:27:52 EET 2011

11.02.2011 19:27:53 connect.SelectData run
SEVERE: null
java.sql.SQLSyntaxErrorException: ORA-01722:

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column

CREATE TABLE "LIONFX"."RBF_DATA"
  (
    "ID" NUMBER NOT NULL ENABLE,
    "OUTY0" FLOAT(126),

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when I change column to VARCHAR2 everything ok.
But outY[] declared as a double.
Please advice.