java - SetLayout Function main purpose -

 public void init_numsolvers() {     (x = 0; x < 9; x++) {         n++;         num[x] = new button("" + n);         add(num[x]);         num[x].setbounds(num_x, num_y, 40, 40);         setlayout(null);         num_x += 40;     } 

why setbounds() function doesn't work without setlayout(null) want understand main purpose of setlayout(null) function

you want read tutorials , api spell out setbounds , setlayout does, briefly:

• the setlayout(...) method allows set layout of container, jpanel, flowlayout, borderlayout, gridlayout, null layout, or whatever layout desired. layout manager helps lay out components held container.
• the setbounds(...) method used set location , size of single component, , useful if null layout used container holds component.
• when set layout null, tell container using no layout @ all, , programmer responsible setting sizes , positions of components added container.
• having said this, should strive avoid using null layouts , setbounds(...). while newbie swing programmer, may seem easiest way create complex layouts, when using them create gui's might on 1 platform only. more importantly, create gui's impossible maintain , upgrade without causing subtle bugs. don't use them if @ possible.
• please read official layout manager tutorials on explained there.

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note code repeatedly sets container's layout null within loop. have no idea why repeatedly since need , want set container's layout once.