Produce random numbers in pairs with java

Hi all i am developing a memory game in java as my homework i want to produce random numbers 1 between number of boxes with pairs.

public void GenerateBoxesGrid(JPanel jp){
       jp.setLayout(new GridLayout(2,4));
       for (int i = 0; i < numberofboxes; i++) {
            int num = generator.nextInt(5);
            button[i] = new JToggleButton();
            button[i].setText(Integer.toString(num));
            button[i].setSize(1,1);
            jp.add(button[i]);
            button[i].setBackground(defaultColor);
            button[i].setVisible(true);

generator object is generating random numbers but without pairs.For example when user wants 6 boxes it should be 1,1,2,2,3,3 on screen.Thanks for your answers.