random platform generator in jumping game

i am making a game with the same concept as the game doodle jump except with a monkey and platforms. i am trying to create the best algorithm to create random platforms, however i keep running into "impossible" situations such as one platform directly on top of another making it impossible to move forth in the game. i am looking for ideas that will help me finesse my algorithm i currently have, which is:

    int prevcount =0;
    int platformcounter=0;
    int numberofplatforms = 5;
    int theplatformputter;
            boolean must =false;
            if(numberofplatforms<=numPlats) {

                for (int first = 97; first >= 1; first--)
                        {

                            grid[98][1] = new     monkeySquare(1,98,monkeySquare.PLAT);
                        platformcounter =0;
                        if (must) {
                            theplatformputter = (int) (Math.random() * (4 - prevcount)) + 1;
                            must = false;
                        } else {
                            theplatformputter = (int) (Math.random() * (5 - prevcount));
                        }
                        for (int xx = 1; xx <= theplatformputter; xx++) {

                            int column = (int) (Math.random() * 5);
                           while (grid[first + 1][column] != null && grid[first+2][column]!=null) {
                                 column = (int) (Math.random() * 5);
                               break;
                            }
                            grid[first][column] = new monkeySquare(column, first, monkeySquare.PLAT);
                            platformcounter++;
                            numberofplatforms++;

                        }
                        prevcount = platformcounter;

                        System.out.println("prevcount is" + prevcount);
                        System.out.println("platcount is"+platformcounter);
                        if(prevcount==0 && platformcounter==0)
                        {
                            System.out.println("must is true :p");
                            must=true;
                        }

                    }

  i appreciate anyone's help. i am in high school and have been working on this game for 2 months and this is one of the few problems i have left. thank you!