Here is the array of all the Java reserved keywords (taken from here and keep being updated from here):

String keywords[] = { "abstract", "assert", "boolean", "break", "byte", "case", "catch", 
    "char", "class", "const", "continue", "default", "do", "double", "else", "extends", 
    "false", "final", "finally", "float", "for", "goto", "if", "implements", "import", 
    "instanceof", "int", "interface", "long", "native", "new", "null", "package", 
    "private", "protected", "public", "return", "short", "static", "strictfp", "super", 
    "switch", "synchronized", "this", "throw", "throws", "transient", "true", "try", 
    "void", "volatile", "while"
};

You have to navigate to the library where is Hashtable class using the JAVA_HOME system variable.

System.getenv("JAVA_HOME");

The java.util.Hashtable (and others) is located at %JAVA_HOME%/jre/lib/rt.jar library.

You have to find a way to extract the package, find the required file, decompile it and read lane by lane (using f.e. Regex). I recommend you to start reading answers of this question.

Unfortunately, there is NO other way.

DO NOT build SQL queries using string concatenation - you should be using bind parameters.

Your query string should be:

query="select * from books where BookName LIKE ?";

and then you can do something like:

Class.forName( "oracle.jdbc.OracleDriver" ); // If you are using the Oracle driver.

Connection con = DriverManager.getConnection(
  "jdbc:oracle:thin:@localhost:1521:XE",
  "username",
  "password"
);

final String query="select * from books where BookName LIKE ?";
PreparedStatement ps = conn.prepareStatement(query);            
ps.setString( 1, "%" + txt1.getText() + "%" );
ResultSet rs = ps.executeQuery();
// Loop through the result set.
// Close statement/connections

(you will need to handle exceptions, etc.)

and:

• You should not need to change the query to swap between MySQL and Oracle (just change the driver and connection string).
• You do not need to escape any single or double quotation marks in the input string.
• You are protected from SQL injection attacks.
• Oracle can cache the query with the bind parameter and does not have to re-parse / re-compile it when the bind parameter changes.

If you are going to write the query as a string then string literals are surrounded by single quotes (not double quotes) in SQL:

query="select * from books where BookName LIKE '%your_string%'";

and you need to make sure that any single quotes in your string are properly escaped (but just use a bind parameter instead).

From axis.apache.org

Basically, Pre-Sort the keywords and store it in an array and using Arrays.binarySearch on your keyword for the good'ol O(logn) complexity

import java.util.Arrays;

    public class MainDemo {
        static final String keywords[] = { "abstract", "assert", "boolean",
                "break", "byte", "case", "catch", "char", "class", "const",
                "continue", "default", "do", "double", "else", "extends", "false",
                "final", "finally", "float", "for", "goto", "if", "implements",
                "import", "instanceof", "int", "interface", "long", "native",
                "new", "null", "package", "private", "protected", "public",
                "return", "short", "static", "strictfp", "super", "switch",
                "synchronized", "this", "throw", "throws", "transient", "true",
                "try", "void", "volatile", "while" };

        public static boolean isJavaKeyword(String keyword) {
            return (Arrays.binarySearch(keywords, keyword) >= 0);
        }

        //Main method
        public static void main(String[] args) {
            System.out.println(isJavaKeyword("void"));

        }

    }

Output:

True

Alternatively, as users @typeracer,@holger suggested in the comments, you can use SourceVersion.isKeyword("void") which uses javax.lang.model.SourceVersion library and Hashset Data structure internally and keeps the list updated for you.