Oracle PL/SQL drop all database tables

gistfile1.sql

BEGIN
  FOR cur IN (SELECT * FROM DBA_TABLES WHERE OWNER = '<YOUR DATABASE NAME>')
  LOOP
    BEGIN
      EXECUTE IMMEDIATE 'DROP TABLE ' || cur.OWNER || '.' || cur.TABLE_NAME || ' CASCADE CONSTRAINT';
      DBMS_OUTPUT.PUT_LINE('SUCCESS: DROP ' || cur.TABLE_NAME);
    EXCEPTION
    WHEN OTHERS THEN
      DBMS_OUTPUT.PUT_LINE('FAILED: DROP ' || cur.TABLE_NAME || ' ' || SQLERRM);
    END;
  END LOOP;
END;

to see DMBS_OUTPUT in SqlDeveloper, click to Veiw > Dmbs Output in menu bar. After press Ctrl+N and select your connection on "Select Connection" popup.