java frame

            int num = Integer.valueOf(jTextField编号.getText());
            String name = jTextField姓名.getText();
            String sex = jTextField性别.getText();            int age = Integer.valueOf(jTextField年龄.getText());我屏蔽掉第四语句，系统编译成功。保留第四句则报错了..
run:
Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: For input string: ""
        at java.lang.NumberFormatException.forInputString(NumberFormatException.java:48)
        at java.lang.Integer.parseInt(Integer.java:468)
        at java.lang.Integer.parseInt(Integer.java:497)
        at clinicpath1.secondframe.提交ActionPerformed(secondframe.java:292)
        at clinicpath1.secondframe.access$000(secondframe.java:24)
        at clinicpath1.secondframe$1.actionPerformed(secondframe.java:110)点击错误行，弹出一个新的类：Integer.java[r/o]