LayoutManager

JPanel main_panel = new JPanel(); // Панель - используется для организации компонентов в окне
        LayoutManager manager = new LayoutManager() {
            @Override
            public void addLayoutComponent(String name, Component comp) {

            }

            @Override
            public void removeLayoutComponent(Component comp) {

            }

            @Override
            public Dimension preferredLayoutSize(Container parent) {
                return null;
            }

            @Override
            public Dimension minimumLayoutSize(Container parent) {
                return null;
            }

            @Override
            public void layoutContainer(Container parent) {

            }
        };

        main_panel.setLayout(manager);
        main_GUI.add(main_panel);