Difference: "throws xyException" and "try/catch"

Is there a difference? Which is it? Would thus be the same for a function:
"functionName throws xyException"
or
"functionName{
try{
catch(xyException){
}

functionName throws xyException
Calling code must call this function in a try and catch block or code won't compile.
functionName{
try{
catch(xyException){
Calling code does not have to put the call to this function in a try and catch block.
public void methodName() throws xEcxeption{
          try{
                    // something
          }catch(Exception e){
                    // try to clean up something
                    // trhow xEcxeption to calling code so that code can do something as well.
                    // like trying an alternative, informing the user or stop executing
}

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    Ive doen pretty much what you said burt now my program isnt working at all. The window comes up but instead of doing something when you click the button it just throws shit loads of exceptions. Heres my abridged code
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    // Grant Brown
    // 22/02/02
    import java.awt.*;
    import java.awt.event.*;
    import java.io.*;
    import java.util.*;
    import javax.swing.*;
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    private JButton update;
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