java Iterator 的用法

Posted jiml

tags:

篇首语：本文由小常识网(cha138.com)小编为大家整理，主要介绍了java Iterator 的用法相关的知识，希望对你有一定的参考价值。

java.util package has public interface Iterator and contains three methods:

  1. boolean hasNext(): It returns true if Iterator has more element to iterate.
  2. 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.
  3. 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:

  1. void add(Object object): It inserts object immediately before the element that is returned by the next( ) function.
  2. boolean hasNext( ): It returns true if the list has a next element.
  3. boolean hasPrevious( ): It returns true if the list has a previous element.
  4. Object next( ): It returns the next element of the list. It throws ‘NoSuchElementException’ if there is no next element in the list.
  5. Object previous( ): It returns the previous element of the list. It throws ‘NoSuchElementException’ if there is no previous element.
  6. 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();
    }
}

 

以上是关于java Iterator 的用法的主要内容，如果未能解决你的问题，请参考以下文章

Java中Iterator用法整理

Java学习之Iterator(迭代器)的一般用法

java Iterator 的用法

Java学习之Iterator(迭代器)的一般用法(转)

Java学习之Iterator(迭代器)的一般用法 （转）

Iterator的用法