编译提醒我使用了未经检查或不安全的操作，这是为什么

[qq_26386215]

import java.awt.*;
import javax.swing.*;

public class Gui7 extends JFrame{


JLabel bq1,bq2;

JComboBox xl1;

JList lb1;

JPanel mb1,mb2;

JScrollPane gd;

public static void main(String [] args) {

Gui7 aa = new Gui7();


}

public Gui7() {



mb1 = new JPanel();

mb2 = new JPanel();

String[] jk = {"shanghai","beijing","nanjing","ningbo"};

xl1 = new JComboBox(jk);

String[] xl = {"high","college","zhuanke","shuoshi","boshi"};

lb1= new JList(xl);

lb1.setVisibleRowCount(3);

gd =new JScrollPane(lb1);

bq1 = new JLabel("Location");

bq2 = new JLabel("xueli");

this.setLayout(new GridLayout(2,1));

mb1.add(bq1);

mb1.add(xl1);

mb2.add(bq2);

mb2.add(gd);

this.add(mb1);

this.add(mb2);


this.setTitle("用户调查");

this.setSize(300,150);

this.setLocation(150,150);

this.setResizable(false);

this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

this.setVisible(true);
}
}

[huntor]

你用的是哪个版本的Java？ JFrame实现了Serializable接口，继承类应该声明private static final long serialVersionUID = ？？？; Java 8中Swing支持类型参数E， 即JList<E>. JComboBox<E>

[尼古拉斯-全蛋]

泛型？？？？

[weixin_42613992]

这些错误大致上都是类型指定不明确的原因