public interface ListIterator
extends Iterator
An iterator for lists that allows the programmer to traverse the list in either direction, modify the list during iteration, and obtain the iterator's current position in the list. A ListIterator has no current element; its cursor position always lies between the element that would be returned by a call to previous() and the element that would be returned by a call to next(). In a list of length n, there are n+1 valid index values, from 0 to n, inclusive.
Note that the remove() and set(Object) methods are not defined in terms of the cursor position; they are defined to operate on the last element returned by a call to next() or previous().
Method Details
1) public boolean hasNext()
Returns true if this list iterator has more elements when traversing the list in the forward direction. (In other words, returns true if next would return an element rather than throwing an exception.)
Specified by:
hasNext in interface Iterator
Returns:
true if the list iterator has more elements when traversing the list in the forward direction.
2) public Object next()
Returns the next element in the list. This method may be called repeatedly to iterate through the list, or intermixed with calls to previous to go back and forth. (Note that alternating calls to next and previous will return the same element repeatedly.)
Specified by:
next in interface Iterator
Returns:
the next element in the list.
Throws:
NoSuchElementException - if the iteration has no next element.
3) public boolean hasPrevious()
Returns true if this list iterator has more elements when traversing the list in the reverse direction. (In other words, returns true if previous would return an element rather than throwing an exception.)
Returns:
true if the list iterator has more elements when traversing the list in the reverse direction.
4) public Object previous()
Returns the previous element in the list. This method may be called repeatedly to iterate through the list backwards, or intermixed with calls to next to go back and forth. (Note that alternating calls to next and previous will return the same element repeatedly.)
Returns:
the previous element in the list.
Throws:
NoSuchElementException - if the iteration has no previous element.
5) public int nextIndex()
Returns the index of the element that would be returned by a subsequent call to next. (Returns list size if the list iterator is at the end of the list.)
Returns:
the index of the element that would be returned by a subsequent call to next, or list size if list iterator is at end of list.
6) public int previousIndex()
Returns the index of the element that would be returned by a subsequent call to previous. (Returns -1 if the list iterator is at the beginning of the list.)
Returns:
the index of the element that would be returned by a subsequent call to previous, or -1 if list iterator is at beginning of list.
7) public void remove()
Removes from the list the last element that was returned by next or previous (optional operation). This call can only be made once per call to next or previous. It can be made only if ListIterator.add has not been called after the last call to next or previous.
Specified by:
remove in interface Iterator
Throws:
UnsupportedOperationException - if the remove operation is not supported by this list iterator.
IllegalStateException - neither next nor previous have been called, or remove or add have been called after the last call to * next or previous.
8) public void set(Object o)
Replaces the last element returned by next or previous with the specified element (optional operation). This call can be made only if neither ListIterator.remove nor ListIterator.add have been called after the last call to next or previous.
Parameters:
o - the element with which to replace the last element returned by next or previous.
Throws:
UnsupportedOperationException - if the set operation is not supported by this list iterator.
ClassCastException - if the class of the specified element prevents it from being added to this list.
IllegalArgumentException - if some aspect of the specified element prevents it from being added to this list.
IllegalStateException - if neither next nor previous have been called, or remove or add have been called after the last call to next or previous.
9) public void add(Object o)
Inserts the specified element into the list (optional operation). The element is inserted immediately before the next element that would be returned by next, if any, and after the next element that would be returned by previous, if any. (If the list contains no elements, the new element becomes the sole element on the list.) The new element is inserted before the implicit cursor: a subsequent call to next would be unaffected, and a subsequent call to previous would return the new element. (This call increases by one the value that would be returned by a call to nextIndex or previousIndex.)
Parameters:
o - the element to insert.
Throws:
UnsupportedOperationException - if the add method is not supported by this list iterator.
ClassCastException - if the class of the specified element prevents it from being added to this list.
IllegalArgumentException - if some aspect of this element prevents it from being added to this list.
Examples
1) The following program traversing a list in either direction and displaying its elements.
import java.util.ArrayList;
import java.util.Iterator;
import java.util.ListIterator;
public class Main {
public static void main(String[] args) {
ArrayList list = new ArrayList();
list.add("one");
list.add("two");
list.add("three");
ListIterator i = list.listIterator();
System.out.println("The forward direction");
while (i.hasNext()) {
System.out.println("index=" + i.nextIndex() + " value=" + i.next());
}
System.out.println("The backward direction");
while (i.hasPrevious()) {
System.out.println("index=" + i.previousIndex() + " value="
+ i.previous());
}
}
}
The output is
The forward direction
index=0 value=one
index=1 value=two
index=2 value=three
The backward direction
index=2 value=three
index=1 value=two
index=0 value=one
2)Use of add(Object o) method
import java.util.ArrayList;
import java.util.Iterator;
import java.util.ListIterator;
public class Main {
public static void main(String[] args) {
ArrayList list = new ArrayList();
list.add("one");
list.add("two");
list.add("three");
ListIterator i = list.listIterator();
while (i.hasNext()) {
if (i.next().equals("two")) {
i.add("four");
}
}
while (i.hasPrevious()) {
if (i.previous().equals("one")) {
i.add("five");
}
}
System.out.println(list);
}
}
The output is
[five, one, two, four, three]
You can see that,the element is inserted immediately before the next element that would be returned by next, if any, and after the next element that would be returned by previous, if any.
3) Use of set(Object o) method
import java.util.ArrayList;
import java.util.Iterator;
import java.util.ListIterator;
public class Main {
public static void main(String[] args) {
ArrayList list = new ArrayList();
list.add("one");
list.add("two");
list.add("three");
ListIterator i = list.listIterator();
while (i.hasNext()) {
if (i.next().equals("two")) {
i.set("TWO");
}
}
System.out.println(list);
}
}
The output is
[one, TWO, three]
You can see that element "two" is replaced with "TWO" .i.e. Replaces the last element returned by next or previous with the specified element
4) Use of remove() method
import java.util.ArrayList;
import java.util.Iterator;
import java.util.ListIterator;
public class Main {
public static void main(String[] args) {
ArrayList list = new ArrayList();
list.add("one");
list.add("two");
list.add("three");
ListIterator i = list.listIterator();
while (i.hasNext()) {
if (i.next().equals("two")) {
i.remove();
}
}
System.out.println(list);
}
}
The output is
[one, three]
The element "two" is removed from the list. i.e.Removes from the list the last element that was returned by next or previous.
extends Iterator
An iterator for lists that allows the programmer to traverse the list in either direction, modify the list during iteration, and obtain the iterator's current position in the list. A ListIterator has no current element; its cursor position always lies between the element that would be returned by a call to previous() and the element that would be returned by a call to next(). In a list of length n, there are n+1 valid index values, from 0 to n, inclusive.
Note that the remove() and set(Object) methods are not defined in terms of the cursor position; they are defined to operate on the last element returned by a call to next() or previous().
Method Details
1) public boolean hasNext()
Returns true if this list iterator has more elements when traversing the list in the forward direction. (In other words, returns true if next would return an element rather than throwing an exception.)
Specified by:
hasNext in interface Iterator
Returns:
true if the list iterator has more elements when traversing the list in the forward direction.
2) public Object next()
Returns the next element in the list. This method may be called repeatedly to iterate through the list, or intermixed with calls to previous to go back and forth. (Note that alternating calls to next and previous will return the same element repeatedly.)
Specified by:
next in interface Iterator
Returns:
the next element in the list.
Throws:
NoSuchElementException - if the iteration has no next element.
3) public boolean hasPrevious()
Returns true if this list iterator has more elements when traversing the list in the reverse direction. (In other words, returns true if previous would return an element rather than throwing an exception.)
Returns:
true if the list iterator has more elements when traversing the list in the reverse direction.
4) public Object previous()
Returns the previous element in the list. This method may be called repeatedly to iterate through the list backwards, or intermixed with calls to next to go back and forth. (Note that alternating calls to next and previous will return the same element repeatedly.)
Returns:
the previous element in the list.
Throws:
NoSuchElementException - if the iteration has no previous element.
5) public int nextIndex()
Returns the index of the element that would be returned by a subsequent call to next. (Returns list size if the list iterator is at the end of the list.)
Returns:
the index of the element that would be returned by a subsequent call to next, or list size if list iterator is at end of list.
6) public int previousIndex()
Returns the index of the element that would be returned by a subsequent call to previous. (Returns -1 if the list iterator is at the beginning of the list.)
Returns:
the index of the element that would be returned by a subsequent call to previous, or -1 if list iterator is at beginning of list.
7) public void remove()
Removes from the list the last element that was returned by next or previous (optional operation). This call can only be made once per call to next or previous. It can be made only if ListIterator.add has not been called after the last call to next or previous.
Specified by:
remove in interface Iterator
Throws:
UnsupportedOperationException - if the remove operation is not supported by this list iterator.
IllegalStateException - neither next nor previous have been called, or remove or add have been called after the last call to * next or previous.
8) public void set(Object o)
Replaces the last element returned by next or previous with the specified element (optional operation). This call can be made only if neither ListIterator.remove nor ListIterator.add have been called after the last call to next or previous.
Parameters:
o - the element with which to replace the last element returned by next or previous.
Throws:
UnsupportedOperationException - if the set operation is not supported by this list iterator.
ClassCastException - if the class of the specified element prevents it from being added to this list.
IllegalArgumentException - if some aspect of the specified element prevents it from being added to this list.
IllegalStateException - if neither next nor previous have been called, or remove or add have been called after the last call to next or previous.
9) public void add(Object o)
Inserts the specified element into the list (optional operation). The element is inserted immediately before the next element that would be returned by next, if any, and after the next element that would be returned by previous, if any. (If the list contains no elements, the new element becomes the sole element on the list.) The new element is inserted before the implicit cursor: a subsequent call to next would be unaffected, and a subsequent call to previous would return the new element. (This call increases by one the value that would be returned by a call to nextIndex or previousIndex.)
Parameters:
o - the element to insert.
Throws:
UnsupportedOperationException - if the add method is not supported by this list iterator.
ClassCastException - if the class of the specified element prevents it from being added to this list.
IllegalArgumentException - if some aspect of this element prevents it from being added to this list.
Examples
1) The following program traversing a list in either direction and displaying its elements.
import java.util.ArrayList;
import java.util.Iterator;
import java.util.ListIterator;
public class Main {
public static void main(String[] args) {
ArrayList list = new ArrayList();
list.add("one");
list.add("two");
list.add("three");
ListIterator i = list.listIterator();
System.out.println("The forward direction");
while (i.hasNext()) {
System.out.println("index=" + i.nextIndex() + " value=" + i.next());
}
System.out.println("The backward direction");
while (i.hasPrevious()) {
System.out.println("index=" + i.previousIndex() + " value="
+ i.previous());
}
}
}
The output is
The forward direction
index=0 value=one
index=1 value=two
index=2 value=three
The backward direction
index=2 value=three
index=1 value=two
index=0 value=one
2)Use of add(Object o) method
import java.util.ArrayList;
import java.util.Iterator;
import java.util.ListIterator;
public class Main {
public static void main(String[] args) {
ArrayList list = new ArrayList();
list.add("one");
list.add("two");
list.add("three");
ListIterator i = list.listIterator();
while (i.hasNext()) {
if (i.next().equals("two")) {
i.add("four");
}
}
while (i.hasPrevious()) {
if (i.previous().equals("one")) {
i.add("five");
}
}
System.out.println(list);
}
}
The output is
[five, one, two, four, three]
You can see that,the element is inserted immediately before the next element that would be returned by next, if any, and after the next element that would be returned by previous, if any.
3) Use of set(Object o) method
import java.util.ArrayList;
import java.util.Iterator;
import java.util.ListIterator;
public class Main {
public static void main(String[] args) {
ArrayList list = new ArrayList();
list.add("one");
list.add("two");
list.add("three");
ListIterator i = list.listIterator();
while (i.hasNext()) {
if (i.next().equals("two")) {
i.set("TWO");
}
}
System.out.println(list);
}
}
The output is
[one, TWO, three]
You can see that element "two" is replaced with "TWO" .i.e. Replaces the last element returned by next or previous with the specified element
4) Use of remove() method
import java.util.ArrayList;
import java.util.Iterator;
import java.util.ListIterator;
public class Main {
public static void main(String[] args) {
ArrayList list = new ArrayList();
list.add("one");
list.add("two");
list.add("three");
ListIterator i = list.listIterator();
while (i.hasNext()) {
if (i.next().equals("two")) {
i.remove();
}
}
System.out.println(list);
}
}
The output is
[one, three]
The element "two" is removed from the list. i.e.Removes from the list the last element that was returned by next or previous.
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