try {
    if (stmt.execute("CREATE TABLE scn_test (value NUMBER)")) {
        System.out.println("Table scn_test is successfully created.");
    }
} catch (SQLSyntaxErrorException e) {
    if (e.getErrorCode() != 955) {
        throw e;
    }
}

select count(*) from ALL_TABLES where table_name='table_name'

create or replace procedure createTableIfNotExists (clauses varchar2) is
    alreadyExists exception;
    pragma exception_init (alreadyExists, -955);
begin
    execute immediate 'create table ' || clauses;
exception when alreadyExists then null;
end createTableIfNotExists;
/
SQL> exec createTableIfNotExists ('testtab (id number, memo varchar (32))')

PL/SQL procedure successfully completed.

SQL> desc testtab

Name Null Type
---- ---- ------------
ID        NUMBER
MEMO      VARCHAR2(32)