訂正

String[] titleName = {"アイテム名","イベント","利益率","調合確率"} ;
JLabel[] titles = new JLabel[4];

for (int i = 0 ; i < 4 ; i++)
titles[i] = new JLabel();

JFrame jFrame = new JFrame();
Container p = jFrame.getContentPane() ;
p.setLayout(new BoxLayout(p, BoxLayout.Y_AXIS));

jFrame.setBounds(1000, 300, 300, 110);

for(int i = 0; i < 4 ; i++) {
titles[i].setText(titleName[i]);
p.add(titles[i]);
}
jFrame.setVisible (true);