Why do I get "Exception; must be caught or declared to be thrown" when I try to compile my Java code? -

import java.awt.*;  import javax.swing.*; import java.awt.event.*; import javax.crypto.*; import javax.crypto.spec.*; import java.security.*; import java.io.*;   public class encrypturl extends japplet implements actionlistener {   container content;   jtextfield username = new jtextfield();      jtextfield firstname = new jtextfield();       jtextfield lastname = new jtextfield();       jtextfield email = new jtextfield();       jtextfield phone = new jtextfield();       jtextfield heartbeatid = new jtextfield();       jtextfield regioncode = new jtextfield();       jtextfield retregioncode = new jtextfield();       jtextfield encryptedtextfield = new jtextfield();      jpanel finishpanel = new jpanel();     public void init() {     //settitle("book - e project");     setsize(800,600);     content = getcontentpane();     content.setbackground(color.yellow);     content.setlayout(new boxlayout(content, boxlayout.y_axis));       jbutton submit = new jbutton("submit");      content.add(new jlabel("user name"));     content.add(username);      content.add(new jlabel("first name"));     content.add(firstname);      content.add(new jlabel("last name"));     content.add(lastname);      content.add(new jlabel("email"));     content.add(email);      content.add(new jlabel("phone"));     content.add(phone);      content.add(new jlabel("heartbeatid"));     content.add(heartbeatid);      content.add(new jlabel("region code"));     content.add(regioncode);      content.add(new jlabel("retregioncode"));     content.add(retregioncode);      content.add(submit);      submit.addactionlistener(this);     }    public void actionperformed(actionevent e) {     if(e.getactioncommand() == "submit"){          string subusername = username.gettext();         string subfname = firstname.gettext();         string sublname = lastname.gettext();         string subemail = email.gettext();         string subphone = phone.gettext();         string subheartbeatid = heartbeatid.gettext();         string subregioncode = regioncode.gettext();         string subretregioncode = retregioncode.gettext();          string concaturl = "user="+ subusername + "&f="+ subfname + "&l=" +sublname+ "&em=" + subemail + "&p="+subphone+"&h="+subheartbeatid+"&re="+subregioncode+ "&ret=" + subretregioncode;         concaturl = padstring(concaturl, ' ', 16);         byte[] encrypted = encrypt(concaturl);         string encryptedstring = bytestohex(encrypted);         content.removeall();         content.add(new jlabel("concatenated user input -->" + concaturl));          content.add(encryptedtextfield);         setcontentpane(content);     }   }    public static byte[] encrypt(string toencrypt) throws exception{     try{       string plaintext = toencrypt;       string key = "01234567890abcde";       string iv = "fedcba9876543210";        secretkeyspec keyspec = new secretkeyspec(key.getbytes(), "aes");       ivparameterspec ivspec = new ivparameterspec(iv.getbytes());        cipher cipher = cipher.getinstance("aes/cbc/nopadding");       cipher.init(cipher.encrypt_mode,keyspec,ivspec);       byte[] encrypted = cipher.dofinal(toencrypt.getbytes());        return encrypted;     }     catch(exception e){      }    }    public static byte[] decrypt(byte[] todecrypt) throws exception{       string key = "01234567890abcde";       string iv = "fedcba9876543210";        secretkeyspec keyspec = new secretkeyspec(key.getbytes(), "aes");       ivparameterspec ivspec = new ivparameterspec(iv.getbytes());        cipher cipher = cipher.getinstance("aes/cbc/nopadding");       cipher.init(cipher.decrypt_mode,keyspec,ivspec);       byte[] decrypted = cipher.dofinal(todecrypt);        return decrypted;   }   public static string bytestohex(byte[] data) {     if (data==null)     {       return null;     }     else     {       int len = data.length;       string str = "";       (int i=0; i<len; i++)       {         if ((data[i]&0xff)<16)           str = str + "0" + java.lang.integer.tohexstring(data[i]&0xff);         else           str = str + java.lang.integer.tohexstring(data[i]&0xff);       }       return str;     }   }   public static string padstring(string source, char paddingchar, int size)   {     int padlength = size-source.length()%size;     (int = 0; < padlength; i++) {       source += paddingchar;     }     return source;   } } 

i'm getting unreported exception

java.lang.exception; must caught or declared thrown byte[] encrypted = encrypt(concaturl); 

as as

.java:109: missing return statement 

can me solving these problems?

all problems derive this

byte[] encrypted = cipher.dofinal(toencrypt.getbytes()); return encrypted; 

which enclosed in try, catch block, problem in case program found exception not returning anything. put (modify program logic stands):

public static byte[] encrypt(string toencrypt) throws exception{     try{         string plaintext = toencrypt;         string key = "01234567890abcde";         string iv = "fedcba9876543210";          secretkeyspec keyspec = new secretkeyspec(key.getbytes(), "aes");         ivparameterspec ivspec = new ivparameterspec(iv.getbytes());          cipher cipher = cipher.getinstance("aes/cbc/nopadding");         cipher.init(cipher.encrypt_mode,keyspec,ivspec);         byte[] encrypted = cipher.dofinal(toencrypt.getbytes());          return encrypted;     } catch(exception e){         return null;            // must return     } } 

for second 1 must catch exception encrypt method call, (also modify program logic stands):

public void actionperformed(actionevent e)   .   .   .     try {         byte[] encrypted = encrypt(concaturl);         string encryptedstring = bytestohex(encrypted);         content.removeall();         content.add(new jlabel("concatenated user input -->" + concaturl));          content.add(encryptedtextfield);     setcontentpane(content);     } catch (exception exc) {         // todo: handle exception     } } 

the lessons must learn this:

• a method return-type must always return object of type, mean in possible scenarios
• all checked exceptions must always handled