java.sql.Connection conn = DriverManager.getConnection("jdbc:sqlite:test.db");
Statement stat = conn.createStatement();
...
String sql = "select * from users WHERE username='" + username + "' AND password='" + password + "';";
...
ResultSet rs = stat.executeQuery(sql);

user1'; insert into users ('username','password') values ('w1','w2');--
user1' or '1'='1'; insert into users values ('w1','w2');--