JButton not performing it's Required Function in java -

here's code of currency converter program . earlier null pointer exception occurred , rectified . there no errors in program . program runs convert button not perform operation . believe problem lies in actionperformed function , i'm not being able identify .

 import java.awt.event.*;     import javax.swing.*;     import java.awt.*;     import java.io.*;        public class trial extends jframe implements actionlistener{            public string[] list={"dollars","euros ","yen","pounds","rupees"};          jpanel panel1 = new jpanel();          jpanel panel2 = new jpanel();         public jcombobox cb,cb1;          public jtextfield tf1;         public jtextfield tf2;         public jlabel label3;         public jlabel label4;          jpanel panel3 = new jpanel();          public jbutton button1;         public jbutton button2;          public trial(){         setlayout(new boxlayout(getcontentpane(),boxlayout.y_axis));              getcontentpane().setlayout(         new boxlayout(getcontentpane(), boxlayout.page_axis)     );           jlabel label1 = new jlabel("from  :");         label1.setfont(new font("serif", font.bold, 15));          jcombobox cb = new jcombobox();           cb= new jcombobox(list);         cb.getselectedindex();         panel1.setbackground(color.red);         panel1.add(label1);         panel1.add(cb);           jlabel label2 = new jlabel("to :");         label2.setfont(new font("serif", font.bold, 15));         jcombobox cb1 = new jcombobox();         cb1=new jcombobox(list);         cb1.getselectedindex();          cb.addactionlistener(this);          cb1.addactionlistener(this);              panel1.add(label2);         panel1.add(cb1);         add(panel1);         jlabel label3 = new jlabel("\n\nenter amount  :");         label3.setfont(new font("serif", font.bold, 15));         jtextfield tf1 = new jtextfield(15);      //  label3.sethorizontalalignment(swingconstants.center);     //  label3.setverticalalignment(swingconstants.center);         panel2.add(label3);         panel2.add(tf1);              jlabel label4 = new jlabel("converted amount :");         label4.setfont(new font("serif", font.bold, 15));         label4.setdisplayedmnemonic(keyevent.vk_o);         jtextfield tf2 = new jtextfield(15);          tf1.addactionlistener(this);              tf2.addactionlistener(this);          panel2.add(label4);         panel2.add(tf2);         panel2.setbackground(color.blue);         add(panel2);          jbutton button1 = new jbutton("convert");         button1.setfont(new font("serif", font.bold, 15));         button1.setmnemonic(keyevent.vk_k);         panel3.add(button1);          jbutton button2 = new jbutton("clear ");         button2.setfont(new font("serif", font.bold, 15));         button2.setmnemonic(keyevent.vk_c);           button1.addactionlistener(this);              button2.addactionlistener(this);              panel3.add(button2);         panel3.setbackground(color.green);          add(panel3);           }          public void actionperformed(actionevent e) {             double a,b=0;              object src = e.getsource();             if(src.equals(button1)){             a=double.valueof(tf1.gettext());             try{                 if(cb.getselectedindex()==0 && cb1.getselectedindex()==1)                     {b=a*0.89;}                 if(cb.getselectedindex()==0 && cb1.getselectedindex()==2)                     {b=a*124.75;}                 if(cb.getselectedindex()==0 && cb1.getselectedindex()==3)                     {b=a*0.65;}                 if(cb.getselectedindex()==0 && cb1.getselectedindex()==4)                     {b=a*64.08;}                 if(cb.getselectedindex()==1 && cb1.getselectedindex()==0)                     {b=a*1.13;}                 if(cb.getselectedindex()==1 && cb1.getselectedindex()==2)                     {b=a*140.49;}                 if(cb.getselectedindex()==1 && cb1.getselectedindex()==3)                     {b=a*0.74;}                 if(cb.getselectedindex()==1 && cb1.getselectedindex()==4)                     {b=a*71.34;}                 if(cb.getselectedindex()==2 && cb1.getselectedindex()==0)                     {b=a*0.0080;}                 if(cb.getselectedindex()==2 && cb1.getselectedindex()==1)                     {b=a*0.0071;}                 if(cb.getselectedindex()==2 && cb1.getselectedindex()==3)                     {b=a*0.0052;}                 if(cb.getselectedindex()==2 && cb1.getselectedindex()==4)                     {b=a*0.51;}                 if(cb.getselectedindex()==3 && cb1.getselectedindex()==0)                     {b=a*1.53;}                 if(cb.getselectedindex()==3 && cb1.getselectedindex()==1)                     {b=a*1.36;}                 if(cb.getselectedindex()==3 && cb1.getselectedindex()==2)                     {b=a*191.26;}                 if(cb.getselectedindex()==3 && cb1.getselectedindex()==4)                     {b=a*97.88;}                 if(cb.getselectedindex()==4 && cb1.getselectedindex()==0)                     {b=a*0.0156;}                 if(cb.getselectedindex()==4 && cb1.getselectedindex()==1)                 {   b=a*0.014;}                 if(cb.getselectedindex()==4 && cb1.getselectedindex()==2)                     {b=a*1.9607;}                 if(cb.getselectedindex()==4 && cb1.getselectedindex()==3)                     {b=a*0.0108;}                  tf2.settext(string.valueof(b));              }catch(exception x){system.out.println("error");}             }             if(src.equals(button2)){                 tf1.settext("0000");                 tf2.settext("0000");                             }          }           } 

you're shadowing variable button1. replace

jbutton button1 = new jbutton("convert"); 

with

button1 = new jbutton("convert");