A set of double quotes identifies string literals in Java, as in the following Java code fragment:
String str = "This is a string";
In SQL, however, single quotes mark strings, and double quotes indicate an identifier, as illustrated by the following SQL statement:
INSERT INTO TABLE DBA.t1 VALUES( 'Hello' );
You should always use the double quote in Java source code, and single quotes in SQL statements.
The following Java code fragment is valid, if used within a Java class.
String str = new java.lang.String( "Brand new object" );