出错祥细：
Exception in thread "main " java.lang.NullPointerException
at awt.GridLayoutTest.init(GridLayoutTest.java:36)
at awt.GridLayoutTest. <init> (GridLayoutTest.java:24)
at awt.GridLayoutTest.main(GridLayoutTest.java:57)
程序如下：
package awt;
import java.awt.Button;
import java.awt.Color;
import java.awt.Frame;
import java.awt.GridLayout;
import java.awt.Panel;
import java.awt.TextField;
public class GridLayoutTest {
Frame frame = null;
Panel pn,pm,pc,ps;
String[] s = { "7 ", "8 ", "9 ", "/ ",
"sprt ", "4 ", "5 ", "6 ",
"* ", "% ", "1 ", "2 ",
"3 ", "- ", "1/x ", "0 ",
"+/- ", ". ", "+ ", "= "};
String[] m = { "MC ", "MR ", "MS ", "M+ "};
Button[] bs = new Button[s.length];
Button[] bm = new Button[m.length];
TextField tf = new TextField( "0. ",150);
public GridLayoutTest() {
init();
}
private void init() {
frame = new Frame( "计算器 v1.0 ");
frame.setLayout(new GridLayout(4,5,3,3));
for(int i=0;i <bs.length;i++)
{
bs[i] = new Button(s[i]);
bs[i].setBackground(Color.LIGHT_GRAY);
bs[i].setForeground(Color.blue);
ps.add(bs[i]);
}
for(int j=0;j <bm.length;j++){
bm[j] = new Button(m[j]);
bm[j].setBackground(Color.LIGHT_GRAY);
bm[j].setForeground(Color.blue);
pm.add(bm[j]);
}
frame.add(pm, "West ");
frame.add(ps, "South ");
frame.setSize(150,150);
frame.pack();
frame.setVisible(true);
}
/**
* @param args
*/
public static void main(String[] args) {
new GridLayoutTest();
}
}
------解决方案--------------------
ps没有初始化，就这样用了：ps.add(bs[i])。
new一个出来。
------解决方案--------------------
1楼正解
Panel pn,pm,pc,ps;这些最好全部初始化