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java Iterator 的用法
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内容图文
java.util package has public interface Iterator and contains three methods:
- boolean hasNext(): It returns true if Iterator has more element to iterate.
- Object next(): It returns the next element in the collection until the hasNext()method return true. This method throws ‘NoSuchElementException’ if there is no next element.
- void remove(): It removes the current element in the collection. This method throws ‘IllegalStateException’ if this function is called before next( ) is invoked.
// Java code to illustrate the use of iterator
import
java.io.*;
import
java.util.*;
class
Test {
public
static
void
main(String[] args)
{
ArrayList<String> list =
new
ArrayList<String>();
list.add(
"A"
);
list.add(
"B"
);
list.add(
"C"
);
list.add(
"D"
);
list.add(
"E"
);
// Iterator to traverse the list
Iterator iterator = list.iterator();
System.out.println(
"List elements : "
);
while
(iterator.hasNext())
System.out.print(iterator.next() +
" "
);
System.out.println();
}
}
|
ListIterator
‘ListIterator’ in Java is an Iterator which allows users to traverse Collection in both direction. It contains the following methods:
- void add(Object object): It inserts object immediately before the element that is returned by the next( ) function.
- boolean hasNext( ): It returns true if the list has a next element.
- boolean hasPrevious( ): It returns true if the list has a previous element.
- Object next( ): It returns the next element of the list. It throws ‘NoSuchElementException’ if there is no next element in the list.
- Object previous( ): It returns the previous element of the list. It throws ‘NoSuchElementException’ if there is no previous element.
- void remove( ): It removes the current element from the list. It throws ‘IllegalStateException’ if this function is called before next( ) or previous( ) is invoked.
// Java code to illustrate the use of ListIterator
import
java.io.*;
import
java.util.*;
class
Test {
public
static
void
main(String[] args)
{
ArrayList<String> list =
new
ArrayList<String>();
list.add(
"A"
);
list.add(
"B"
);
list.add(
"C"
);
list.add(
"D"
);
list.add(
"E"
);
// ListIterator to traverse the list
ListIterator iterator = list.listIterator();
// Traversing the list in forward direction
System.out.println(
"Displaying list elements in forward direction : "
);
while
(iterator.hasNext())
System.out.print(iterator.next() +
" "
);
System.out.println();
// Traversing the list in backward direction
System.out.println(
"Displaying list elements in backward direction : "
);
while
(iterator.hasPrevious())
System.out.print(iterator.previous() +
" "
);
System.out.println();
}
}
|
详见https://docs.oracle.com/javase/8/docs/api/java/util/Iterator.html
// Java code to illustrate the use of ListIterator
import
java.io.*;
import
java.util.*;
class
Test {
public
static
void
main(String[] args)
{
ArrayList<String> list =
new
ArrayList<String>();
list.add(
"A"
);
list.add(
"B"
);
list.add(
"C"
);
list.add(
"D"
);
list.add(
"E"
);
// ListIterator to traverse the list
ListIterator iterator = list.listIterator();
// Traversing the list in forward direction
System.out.println(
"Displaying list elements in forward direction : "
);
while
(iterator.hasNext())
System.out.print(iterator.next() +
" "
);
System.out.println();
// Traversing the list in backward direction
System.out.println(
"Displaying list elements in backward direction : "
);
while
(iterator.hasPrevious())
System.out.print(iterator.previous() +
" "
);
System.out.println();
}
}
|
原文：https://www.cnblogs.com/jiml/p/9357021.html
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