- You have a code fragment that can be grouped together.
Turn the fragment into a method whose name explains the purpose of the method.
Example: No Local Variables
before
// print banner
System.out.println ("**************************");
System.out.println ("***** Customer Owes ******");
System.out.println ("**************************");
after
printBanner();
void printBanner() {
// print banner
System.out.println ("**************************");
System.out.println ("***** Customer Owes ******");
System.out.println ("**************************");
}
http://sourcemaking.com/refactoring/extract-method
- The Extract Method refactoring has the following limitations:
Refactoring does not work with multiple output values in automatic mode. You have to change your code before applying the refactoring.
Refactoring does not work for a code fragment which conditionally returns from the containing method and is not placed at the end of it.
before (eclipse)
public class ExtractMethod1 {
public static void main(String[] args) {
method1();
}
static void method1() {
int a=1;
int b=2;
int c=a+b;
int d=a+c;
}
}
after (eclipse)
public class ExtractMethod1 {
public static void main(String[] args) {
method1();
}
static void method1() {
getSum();
}
private static void getSum() {
int a=1;
int b=2;
int c=a+b;
int d=a+c;
}
}
In Eclipse you select the code fragment you want to refactor,right click,refactor and extract method
before (IntelliJ IDEA 11.1)
public class ExtractMethod1 {
public static void main(String[] args) {
method1();
}
static void method1() {
int a=1;
int b=2;
int c=a+b;
int d=a+c;
}
}
after (IntelliJ IDEA 11.1)
public class ExtractMethod1 {
public static void main(String[] args) {
method1();
}
static void method1() {
int a=1;
int b=2;
int c=add(a,b);
int d=add(a,c);
}
private static int add(int a,int b) {
return a+b;
}
}
before (IntelliJ IDEA 11.1)
ArrayList method2()
{
String[] strings={"a","b","c","d"};
ArrayList list=new ArrayList();
for (int i = 0; i < strings.length; i++) {
list.add(strings[i]);
}
return list;
}
}
after (IntelliJ IDEA 11.1)
private ArrayList add(String[] strings)
{
ArrayList list=new ArrayList();
for (int i = 0; i < strings.length; i++) {
list.add(strings[i]);
}
return list;
}
http://www.jetbrains.com/idea/webhelp/extract-method.html#h2example
- Extract Method
The Extract Method refactoring allows you to select a block of code and convert it to a method. Eclipse automatically infers the method arguments and return types.
This is useful when a method is too big and you want to subdivide blocks of it into different methods. It is also useful if you have a piece of code that is reused across many methods. When you select one of those blocks of code and do a refactoring, Eclipse finds other occurrences of that block of code and replaces it with a call to the new method.
Listing 3. Before Extract Method refactoring
@Override
public Object get(Object key)
{
TimedKey timedKey = new TimedKey(System.currentTimeMillis(), key);
Object object = map.get(timedKey);
if (object != null)
{
/**
* if this was removed after the 'get' call by the worker thread
* put it back in
*/
map.put(timedKey, object);
return object;
}
return null;
}
Listing 4. After Before Extract Method refactoring
@Override
public Object get(Object key)
{
TimedKey timedKey = new TimedKey(System.currentTimeMillis(), key);
Object object = map.get(timedKey);
return putIfNotNull(timedKey, object);
}
private Object putIfNotNull(TimedKey timedKey, Object object)
{
if (object != null)
{
/**
* if this was removed after the 'get' call by the worker thread
* put it back in
*/
map.put(timedKey, object);
return object;
}
return null;
}
http://www.ibm.com/developerworks/opensource/library/os-eclipse-refactoring/index.html
