Java 尝试运行JFrame时获取空点异常
从Java 尝试运行JFrame时获取空点异常,java,swing,nullpointerexception,Java,Swing,Nullpointerexception,从public void Performance()中删除void 您需要的是构造函数,而不是void方法 该错误是由于没有实例化对象造成的。以下是代码性能类,请使用以下内容替换您的性能类: import java.awt.*; import javax.swing.*; class Performance{ private JLabel l1; private JLabel l2; private JLabel l3; private JLabel l4; pri
public void Performance()中删除void
您需要的是构造函数,而不是void方法
该错误是由于没有实例化对象造成的。以下是代码性能类,请使用以下内容替换您的性能类:
import java.awt.*;
import javax.swing.*;
class Performance{
private JLabel l1;
private JLabel l2;
private JLabel l3;
private JLabel l4;
private JLabel l5;
private JLabel l6;
private JLabel l7;
private JLabel l8;
private JLabel l9;
private JComboBox c1;
private JComboBox c2;
private JComboBox c3;
private JComboBox c4;
private JComboBox c5;
private JComboBox c6;
private JComboBox c7;
private JComboBox c8;
private JComboBox c9;
private String s1[] ={"S","A","B","C","D","E","U"};
private String s2[] ={"S","A","B","C","D","E","U"};
private String s3[] ={"S","A","B","C","D","E","U"};
private String s4[] ={"S","A","B","C","D","E","U"};
private String s5[] ={"S","A","B","C","D","E","U"};
private String s6[] ={"S","A","B","C","D","E","U"};
private String s7[] ={"S","A","B","C","D","E","U"};
private String s8[] ={"S","A","B","C","D","E","U"};
private String s9[] ={"S","A","B","C","D","E","U"};
private JButton submit;
private JFrame f;
public void Performance(){
f = new JFrame("CGPA calc for cse sem6");
l1 = new JLabel("AI");
l2 = new JLabel("PCD");
l3 = new JLabel("OOAD");
l4 = new JLabel("ACA");
l5 = new JLabel("WT");
l6 = new JLabel("KM");
l7 = new JLabel("LAB1");
l8 = new JLabel("LAB2");
l9 = new JLabel("LAB3");
c1 = new JComboBox(s1);
c2 = new JComboBox(s2);
c3 = new JComboBox(s3);
c4 = new JComboBox(s4);
c5 = new JComboBox(s5);
c6 = new JComboBox(s6);
c7 = new JComboBox(s7);
c8 = new JComboBox(s8);
c9 = new JComboBox(s9);
submit = new JButton("Submit");
}
public void Lancher(){
f.setLayout(new GridLayout(10,2,10,10));
f.setVisible(true);
f.setSize(300,300);
f.add(l1);
f.add(c1);
f.add(l2);
f.add(c2);
f.add(l3);
f.add(c3);
f.add(l4);
f.add(c4);
f.add(l5);
f.add(c5);
f.add(l6);
f.add(c6);
f.add(l7);
f.add(c7);
f.add(l8);
f.add(c8);
f.add(l9);
f.add(c9);
f.add(submit);
}
}
public class cse_sem6
{
public static void main(String a[]){
Performance obj = new Performance();
obj.Lancher();
}
}
}始终复制/粘贴错误或异常输出。在哪一行获得异常?@Seb堆栈跟踪将解释这一点以及更多。添加所有组件后,移动setVisible属性。看看是否有帮助。
class Performance{
private JLabel l1;
private JLabel l2;
private JLabel l3;
private JLabel l4;
private JLabel l5;
private JLabel l6;
private JLabel l7;
private JLabel l8;
private JLabel l9;
private JComboBox c1;
private JComboBox c2;
private JComboBox c3;
private JComboBox c4;
private JComboBox c5;
private JComboBox c6;
private JComboBox c7;
private JComboBox c8;
private JComboBox c9;
private String s1[] ={"S","A","B","C","D","E","U"};
private String s2[] ={"S","A","B","C","D","E","U"};
private String s3[] ={"S","A","B","C","D","E","U"};
private String s4[] ={"S","A","B","C","D","E","U"};
private String s5[] ={"S","A","B","C","D","E","U"};
private String s6[] ={"S","A","B","C","D","E","U"};
private String s7[] ={"S","A","B","C","D","E","U"};
private String s8[] ={"S","A","B","C","D","E","U"};
private String s9[] ={"S","A","B","C","D","E","U"};
private JButton submit;
private JFrame f;
public Performance(){
f = new JFrame("CGPA calc for cse sem6");
l1 = new JLabel("AI");
l2 = new JLabel("PCD");
l3 = new JLabel("OOAD");
l4 = new JLabel("ACA");
l5 = new JLabel("WT");
l6 = new JLabel("KM");
l7 = new JLabel("LAB1");
l8 = new JLabel("LAB2");
l9 = new JLabel("LAB3");
c1 = new JComboBox(s1);
c2 = new JComboBox(s2);
c3 = new JComboBox(s3);
c4 = new JComboBox(s4);
c5 = new JComboBox(s5);
c6 = new JComboBox(s6);
c7 = new JComboBox(s7);
c8 = new JComboBox(s8);
c9 = new JComboBox(s9);
submit = new JButton("Submit");
}
public void Lancher(){
f=new JFrame();
f.setLayout(new GridLayout(10,2,10,10));
f.setVisible(true);
f.setSize(300,300);
f.add(l1);
f.add(c1);
f.add(l2);
f.add(c2);
f.add(l3);
f.add(c3);
f.add(l4);
f.add(c4);
f.add(l5);
f.add(c5);
f.add(l6);
f.add(c6);
f.add(l7);
f.add(c7);
f.add(l8);
f.add(c8);
f.add(l9);
f.add(c9);
f.add(submit);
}