List集合遍历的五种方法

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List集合遍历的五种方法:

public static void main(String[] args) 
    List<Integer> list = Lists.newArrayList();
    list.add(1);
    list.add(2);
    list.add(3);

    //方法一 普通for循环遍历
    System.out.println("普通for循环遍历");
    for (int i = 0; i < list.size(); i++) 
        System.out.println(list.get(i));
    

    //方法二 增强for (也称for each循环)是JDK1.5以后出来的一个高级for循环,专门用来遍历数组和集合的。
    //内部原理其实是个Iterator迭代器,所以在遍历的过程中,不能对集合中的元素进行增删操作。
    System.out.println("增强for");
    for (int i : list) 
        System.out.println(i);
    

    //方法三 Lambda
    System.out.println("Lambda");
    list.forEach(e -> 
        System.out.println(e);
    );

    list.stream().forEach(e -> 
        System.out.println(e);
    );

    //方法四 倒序遍历
    System.out.println("倒序遍历");
    for (int i = list.size() - 1; i >= 0; i--) 
        System.out.println(list.get(i));
    

    //方法五 迭代器遍历
    System.out.println("迭代器遍历");
    Iterator<Integer> it = list.iterator();
    while (it.hasNext()) 
        System.out.println(it.next());
    

    //方法六 List集合自带迭代器
    System.out.println("List集合自带迭代器");
    ListIterator<Integer> listIterator = list.listIterator();
    while(listIterator.hasNext())
        System.out.println(listIterator.next());
    

扩展

List接口概述

List是有序的 Collection(有时称为序列)。列表可能包含重复的元素。除了继承自 的操作外Collection,该List接口还包括以下操作:

Positional access— 根据元素在列表中的数字位置操作元素。诸如get、 set、add、addAll和remove 等方法。

Search— 在列表中搜索指定对象并返回其数字位置。搜索方法包括 indexOf和lastIndexOf。

Iteration— 扩展Iterator语义以利用列表的顺序性。listIterator方法提供了这种行为。

Range-view— 该方法对列表sublist执行任意范围操作。

Java 平台包含两个通用List实现。 ArrayList是性能更好的实现,并且 LinkedList在某些情况下提供更好的性能。

List操作

list1.addAll(list2);
List<Type> list3 = new ArrayList<Type>(list1);
list3.addAll(list2);
List<String> list = people.stream()
.map(Person::getName)
.collect(Collectors.toList());

与 Set接口一样,List加强了对equals和hashCode方法的要求,以便List可以比较两个对象的逻辑相等性,而无需考虑它们的实现类。如果两个List对象以相同的顺序包含相同的元素,则它们是相等的。

List位置访问和搜索操作

基本位置访问运算:

get、set、add、remove(set和remove操作返回被覆盖或删除的旧值)。
indexOf和lastIndexOf返回列表中指定元素的第一个或最后一个索引。
addAll 操作从指定位置开始插入指定 Collection 的所有元素。

交换列表中两个索引值:

第一种:

public static <E> void swap(List<E> a, int i, int j)  
    E tmp = a.get(i); 
    a.set(i, a.get(j)); 
    a.set(j, tmp); 

这是一种多态算法:它交换 List 中的任意两个元素,而不管其实现类型如何。
第二种:

public static void shuffle(List<?> list, Random rnd)  
    for (int i = list.size(); i > 1; i--) 
        swap(list, i - 1, rnd.nextInt(i)); 

该算法在Collections 类中,使用指定的随机源随机排列指定的列表。它从底部向上运行列表,反复将随机选择的元素交换到当前位置。
案列:

public class Shuffle  
    public static void main(String[] args)  
        List<String> list = new ArrayList<String>(); 
        for (String a : args) 
            list.add(a); 
        Collections.shuffle(list, new Random()); 
        System.out.println(list); 
     

Arrays 类中asList 是静态工厂方法,它允许将数组视为 List。此方法不复制数组。 List 中的更改会写入数组,反之亦然。生成的 List 不是通用的 List 实现,因为它没有实现添加和删除操作:数组不可调整大小。利用 Arrays.asList 并调用使用默认随机源的 shuffle 库版本,以下方法与上面方法作用一样,但效率更高。

public class Shuffle 
    public static void main(String[] args) 
        List<String> list = Arrays.asList(args);
        Collections.shuffle(list);
        System.out.println(list);
    

ListIterator

List还提供了一个更丰富的迭代器ListIterator,它可以在任一方向遍历列表,在迭代过程中修改列表,并获取迭代器的当前位置。

// List Iterators
ListIterator<E> listIterator();

ListIterator<E> listIterator(int index);

向后遍历列表:

for (ListIterator<Type> it = list.listIterator(list.size()); it.hasPrevious(); ) 
    Type t = it.previous();
    ...

ListIterator与Iterator关系:

Iterator 可遍历集合 Set 和 List, ListIterator 只能遍历 List。

Iterator 只能单向遍历;ListIterator 可双向遍历。

ListIterator 继承自 Iterator 接口,增加了新的方法,比如添加一个元素、替换一个元素、获取前面或后面元素的索引位置。

List算法

Collections为List提供了更容易操作的算法:

sort — 使用合并排序算法对 List 进行排序,该算法提供快速、稳定的排序。 (稳定排序是不对相等元素重新排序的排序。)

shuffle — 随机排列 List 中的元素。

reverse — 反转 List 中元素的顺序。

rotate — 将 List 中的所有元素旋转指定距离。

swap——交换列表中指定位置的元素。

replaceAll — 将所有出现的一个指定值替换为另一个。

fill — 用指定的值覆盖 List 中的每个元素。

copy — 将源列表复制到目标列表中。

binarySearch — 使用二分搜索算法在有序列表中搜索元素。

indexOfSubList — 返回一个 List 中与另一个 List 相等的第一个子列表的索引。

lastIndexOfSubList — 返回一个 List 的最后一个与另一个 List 相等的子列表的索引。

一切回归源码

package java.util;

import java.util.function.UnaryOperator;

/**
 * An ordered collection (also known as a <i>sequence</i>).  The user of this
 * interface has precise control over where in the list each element is
 * inserted.  The user can access elements by their integer index (position in
 * the list), and search for elements in the list.<p>
 *
 * Unlike sets, lists typically allow duplicate elements.  More formally,
 * lists typically allow pairs of elements <tt>e1</tt> and <tt>e2</tt>
 * such that <tt>e1.equals(e2)</tt>, and they typically allow multiple
 * null elements if they allow null elements at all.  It is not inconceivable
 * that someone might wish to implement a list that prohibits duplicates, by
 * throwing runtime exceptions when the user attempts to insert them, but we
 * expect this usage to be rare.<p>
 *
 * The <tt>List</tt> interface places additional stipulations, beyond those
 * specified in the <tt>Collection</tt> interface, on the contracts of the
 * <tt>iterator</tt>, <tt>add</tt>, <tt>remove</tt>, <tt>equals</tt>, and
 * <tt>hashCode</tt> methods.  Declarations for other inherited methods are
 * also included here for convenience.<p>
 *
 * The <tt>List</tt> interface provides four methods for positional (indexed)
 * access to list elements.  Lists (like Java arrays) are zero based.  Note
 * that these operations may execute in time proportional to the index value
 * for some implementations (the <tt>LinkedList</tt> class, for
 * example). Thus, iterating over the elements in a list is typically
 * preferable to indexing through it if the caller does not know the
 * implementation.<p>
 *
 * The <tt>List</tt> interface provides a special iterator, called a
 * <tt>ListIterator</tt>, that allows element insertion and replacement, and
 * bidirectional access in addition to the normal operations that the
 * <tt>Iterator</tt> interface provides.  A method is provided to obtain a
 * list iterator that starts at a specified position in the list.<p>
 *
 * The <tt>List</tt> interface provides two methods to search for a specified
 * object.  From a performance standpoint, these methods should be used with
 * caution.  In many implementations they will perform costly linear
 * searches.<p>
 *
 * The <tt>List</tt> interface provides two methods to efficiently insert and
 * remove multiple elements at an arbitrary point in the list.<p>
 *
 * Note: While it is permissible for lists to contain themselves as elements,
 * extreme caution is advised: the <tt>equals</tt> and <tt>hashCode</tt>
 * methods are no longer well defined on such a list.
 *
 * <p>Some list implementations have restrictions on the elements that
 * they may contain.  For example, some implementations prohibit null elements,
 * and some have restrictions on the types of their elements.  Attempting to
 * add an ineligible element throws an unchecked exception, typically
 * <tt>NullPointerException</tt> or <tt>ClassCastException</tt>.  Attempting
 * to query the presence of an ineligible element may throw an exception,
 * or it may simply return false; some implementations will exhibit the former
 * behavior and some will exhibit the latter.  More generally, attempting an
 * operation on an ineligible element whose completion would not result in
 * the insertion of an ineligible element into the list may throw an
 * exception or it may succeed, at the option of the implementation.
 * Such exceptions are marked as "optional" in the specification for this
 * interface.
 *
 * <p>This interface is a member of the
 * <a href="@docRoot/../technotes/guides/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @param <E> the type of elements in this list
 *
 * @author  Josh Bloch
 * @author  Neal Gafter
 * @see Collection
 * @see Set
 * @see ArrayList
 * @see LinkedList
 * @see Vector
 * @see Arrays#asList(Object[])
 * @see Collections#nCopies(int, Object)
 * @see Collections#EMPTY_LIST
 * @see AbstractList
 * @see AbstractSequentialList
 * @since 1.2
 */

public interface List<E> extends Collection<E> 
    // Query Operations

    /**
     * Returns the number of elements in this list.  If this list contains
     * more than <tt>Integer.MAX_VALUE</tt> elements, returns
     * <tt>Integer.MAX_VALUE</tt>.
     *
     * @return the number of elements in this list
     */
    int size();

    /**
     * Returns <tt>true</tt> if this list contains no elements.
     *
     * @return <tt>true</tt> if this list contains no elements
     */
    boolean isEmpty();

    /**
     * Returns <tt>true</tt> if this list contains the specified element.
     * More formally, returns <tt>true</tt> if and only if this list contains
     * at least one element <tt>e</tt> such that
     * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>.
     *
     * @param o element whose presence in this list is to be tested
     * @return <tt>true</tt> if this list contains the specified element
     * @throws ClassCastException if the type of the specified element
     *         is incompatible with this list
     * (<a href="Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException if the specified element is null and this
     *         list does not permit null elements
     * (<a href="Collection.html#optional-restrictions">optional</a>)
     */
    boolean contains(Object o);

    /**
     * Returns an iterator over the elements in this list in proper sequence.
     *
     * @return an iterator over the elements in this list in proper sequence
     */
    Iterator<E> iterator();

    /**
     * Returns an array containing all of the elements in this list in proper
     * sequence (from first to last element).
     *
     * <p>The returned array will be "safe" in that no references to it are
     * maintained by this list.  (In other words, this method must
     * allocate a new array even if this list is backed by an array).
     * The caller is thus free to modify the returned array.
     *
     * <p>This method acts as bridge between array-based and collection-based
     * APIs.
     *
     * @return an array containing all of the elements in this list in proper
     *         sequence
     * @see Arrays#asList(Object[])
     */
    Object[] toArray();

    /**
     * Returns an array containing all of the elements in this list in
     * proper sequence (from first to last element); the runtime type of
     * the returned array is that of the specified array.  If the list fits
     * in the specified array, it is returned therein.  Otherwise, a new
     * array is allocated with the runtime type of the specified array and
     * the size of this list.
     *
     * <p>If the list fits in the specified array with room to spare (i.e.,
     * the array has more elements than the list), the element in the array
     * immediately following the end of the list is set to <tt>null</tt>.
     * (This is useful in determining the length of the list <i>only</i> if
     * the caller knows that the list does not contain any null elements.)
     *
     * <p>Like the @link #toArray() method, this method acts as bridge between
     * array-based and collection-based APIs.  Further, this method allows
     * precise control over the runtime type of the output array, and may,
     * under certain circumstances, be used to save allocation costs.
     *
     * <p>Suppose <tt>x</tt> is a list known to contain only strings.
     * The following code can be used to dump the list into a newly
     * allocated array of <tt>String</tt>:
     *
     * <pre>@code
     *     String[] y = x.toArray(new String[0]);
     * </pre>
     *
     * Note that <tt>toArray(new Object[0])</tt> is identical in function to
     * <tt>toArray()</tt>.
     *
     * @param a the array into which the elements of this list are to
     *          be stored, if it is big enough; otherwise, a new array of the
     *          same runtime type is allocated for this purpose.
     * @return an array containing the elements of this list
     * @throws ArrayStoreException if the runtime type of the specified array
     *         is not a supertype of the runtime type of every element in
     *         this list
     * @throws NullPointerException if the specified array is null
     */
    <T> T[] toArray(T[] a);


    // Modification Operations

    /**
     * Appends the specified element to the end of this list (optional
     * operation).
     *
     * <p>Lists that support this operation may place limitations on what
     * elements may be added to this list.  In particular, some
     * lists will refuse to add null elements, and others will impose
     * restrictions on the type of elements that may be added.  List
     * classes should clearly specify in their documentation any restrictions
     * on what elements may be added.
     *
     * @param e element to be appended to this list
     * @return <tt>true</tt> (as specified by @link Collection#add)
     * @throws UnsupportedOperationException if the <tt>add</tt> operation
     *         is not supported by this list
     * @throws ClassCastException if the class of the specified element
     *         prevents it from being added to this list
     * @throws NullPointerException if the specified element is null and this
     *         list does not permit null elements
     * @throws IllegalArgumentException if some property of this element
     *         prevents it from being added to this list
     */
    boolean add(E e);

    /**
     * Removes the first occurrence of the specified element from this list,
     * if it is present (optional operation).  If this list does not contain
     * the element, it is unchanged.  More formally, removes the element with
     * the lowest index <tt>i</tt> such that
     * <tt>(o==null&nbsp;?&nbsp;get(i)==null&nbsp;:&nbsp;o.equals(get(i)))</tt>
     * (if such an element exists).  Returns <tt>true</tt> if this list
     * contained the specified element (or equivalently, if this list changed
     * as a result of the call).
     *
     * @param o element to be removed from this list, if present
     * @return <tt>true</tt> if this list contained the specified element
     * @throws ClassCastException if the type of the specified element
     *         is incompatible with this list
     * (<a href="Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException if the specified element is null and this
     *         list does not permit null elements
     * (<a href="Collection.html#optional-restrictions">optional</a>)
     * @throws UnsupportedOperationException if the <tt>remove</tt> operation
     *         is not supported by this list
     */
    boolean remove(Object o);


    // Bulk Modification Operations

    /**
     * Returns <tt>true</tt> if this list contains all of the elements of the
     * specified collection.
     *
     * @param  c collection to be checked for containment in this list
     * @return <tt>true</tt> if this list contains all of the elements of the
     *         specified collection
     * @throws ClassCastException if the types of one or more elements
     *         in the specified collection are incompatible with this
     *         list
     * (<a href="Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException if the specified collection contains one
     *         or more null elements and this list does not permit null
     *         elements
     *         (<a href="Collection.html#optional-restrictions">optional</a>),
     *         or if the specified collection is null
     * @see #contains(Object)
     */
    boolean containsAll(Collection<?> c);

    /**
     * Appends all of the elements in the specified collection to the end of
     * this list, in the order that they are returned by the specified
     * collection's iterator (optional operation).  The behavior of this
     * operation is undefined if the specified collection is modified while
     * the operation is in progress.  (Note that this will occur if the
     * specified collection is this list, and it's nonempty.)
     *
     * @param c collection containing elements to be added to this list
     * @return <tt>true</tt> if this list changed as a result of the call
     * @throws UnsupportedOperationException if the <tt>addAll</tt> operation
     *         is not supported by this list
     * @throws ClassCastException if the class of an element of the specified
     *         collection prevents it from being added to this list
     * @throws NullPointerException if the specified collection contains one
     *         or more null elements and this list does not permit null
     *         elements, or if the specified collection is null
     * @throws IllegalArgumentException if some property of an element of the
     *         specified collection prevents it from being added to this list
     * @see #add(Object)
     */
    boolean addAll(Collection<? extends E> c);

    /**
     * Inserts all of the elements in the specified collection into this
     * list at the specified position (optional operation).  Shifts the
     * element currently at that position (if any) and any subsequent
     * elements to the right (increases their indices).  The new elements
     * will appear in this list in the order that they are returned by the
     * specified collection's iterator.  The behavior of this operation is
     * undefined if the specified collection is modified while the
     * operation is in progress.  (Note that this will occur if the specified
     * collection is this list, and it's nonempty.)
     *
     * @param index index at which to insert the first element from the
     *              specified collection
     * @param c collection containing elements to be added to this list
     * @return <tt>true</tt> if this list changed as a result of the call
     * @throws UnsupportedOperationException if the <tt>addAll</tt> operation
     *         is not supported by this list
     * @throws ClassCastException if the class of an element of the specified
     *         collection prevents it from being added to this list
     * @throws NullPointerException if the specified collection contains one
     *         or more null elements and this list does not permit null
     *         elements, or if the specified collection is null
     * @throws IllegalArgumentException if some property of an element of the
     *         specified collection prevents it from being added to this list
     * @throws IndexOutOfBoundsException if the index is out of range
     *         (<tt>index &lt; 0 || index &gt; size()</tt>)
     */
    boolean addAll(int index, Collection<? extends E> c);

    /**
     * Removes from this list all of its elements that are contained in the
     * specified collection (optional operation).
     *
     * @param c collection containing elements to be removed from this list
     * @return <tt>true</tt> if this list changed as a result of the call
     * @throws UnsupportedOperationException if the <tt>removeAll</tt> operation
     *         is not supported by this list
     * @throws ClassCastException if the class of an element of this list
     *         is incompatible with the specified collection
     * (<a href="Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException if this list contains a null element and the
     *         specified collection does not permit null elements
     *         (<a href="Collection.html#optional-restrictions">optional</a>),
     *         or if the specified collection is null
     * @see #remove(Object)
     * @see #contains(Object)
     */
    boolean removeAll(Collection<?> c);

    /**
     * Retains only the elements in this list that are contained in the
     * specified collection (optional operation).  In other words, removes
     * from this list all of its elements that are not contained in the
     * specified collection.
     *
     * @param c collection containing elements to be retained in this list
     * @return <tt>true</tt> if this list changed as a result of the call
     * @throws UnsupportedOperationException if the <tt>retainAll</tt> operation
     *         is not supported by this list
     * @throws ClassCastException if the class of an element of this list
     *         is incompatible with the specified collection
     * (<a href="Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException if this list contains a null element and the
     *         specified collection does not permit null elements
     *         (<a href="Collection.html#optional-restrictions">optional</a>),
     *         or if the specified collection is null
     * @see #remove(Object)
     * @see #contains(Object)
     */
    boolean retainAll(Collection<?> c);

    /**
     * Replaces each element of this list with the result of applying the
     * operator to that element.  Errors or runtime exceptions thrown by
     * the operator are relayed to the caller.
     *
     * @implSpec
     * The default implementation is equivalent to, for this @code list:
     * <pre>@code
     *     final ListIterator<E> li = list.listIterator();
     *     while (li.hasNext()) 
     *         li.set(operator.apply(li.next()));
     *     
     * </pre>
     *
     * If the list's list-iterator does not support the @code set operation
     * then an @code UnsupportedOperationException will be thrown when
     * replacing the first element.
     *
     * @param operator the operator to apply to each element
     * @throws UnsupportedOperationException if this list is unmodifiable.
     *         Implementations may throw this exception if an element
     *         cannot be replaced or if, in general, modification is not
     *         supported
     * @throws NullPointerException if the specified operator is null or
     *         if the operator result is a null value and this list does
     *         not permit null elements
     *         (<a href="Collection.html#optional-restrictions">optional</a>)
     * @since 1.8
     */
    default void replaceAll(UnaryOperator<E> operator) 
        Objects.requireNonNull(operator);
        final ListIterator<E> li = this.listIterator();
        while (li.hasNext()) 
            li.set(operator.apply(li.next()));
        
    

    /**
     * Sorts this list according to the order induced by the specified
     * @link Comparator.
     *
     * <p>All elements in this list must be <i>mutually comparable</i> using the
     * specified comparator (that is, @code c.compare(e1, e2) must not throw
     * a @code ClassCastException for any elements @code e1 and @code e2
     * in the list).
     *
     * <p>If the specified comparator is @code null then all elements in this
     * list must implement the @link Comparable interface and the elements'
     * @linkplain Comparable natural ordering should be used.
     *
     * <p>This list must be modifiable, but need not be resizable.
     *
     * @implSpec
     * The default implementation obtains an array containing all elements in
     * this list, sorts the array, and iterates over this list resetting each
     * element from the corresponding position in the array. (This avoids the
     * n<sup>2</sup> log(n) performance that would result from attempting
     * to sort a linked list in place.)
     *
     * @implNote
     * This implementation is a stable, adaptive, iterative mergesort that
     * requires far fewer than n lg(n) comparisons when the input array is
     * partially sorted, while offering the performance of a traditional
     * mergesort when the input array is randomly ordered.  If the input array
     * is nearly sorted, the implementation requires approximately n
     * comparisons.  Temporary storage requirements vary from a small constant
     * for nearly sorted input arrays to n/2 object references for randomly
     * ordered input arrays.
     *
     * <p>The implementation takes equal advantage of ascending and
     * descending order in its input array, and can take advantage of
     * ascending and descending order in different parts of the same
     * input array.  It is well-suited to merging two or more sorted arrays:
     * simply concatenate the arrays and sort the resulting array.
     *
     * <p>The implementation was adapted from Tim Peters's list sort for Python
     * (<a href="http://svn.python.org/projects/python/trunk/Objects/listsort.txt">
     * TimSort</a>).  It uses techniques from Peter McIlroy's "Optimistic
     * Sorting and Information Theoretic Complexity", in Proceedings of the
     * Fourth Annual ACM-SIAM Symposium on Discrete Algorithms, pp 467-474,
     * January 1993.
     *
     * @param c the @code Comparator used to compare list elements.
     *          A @code null value indicates that the elements'
     *          @linkplain Comparable natural ordering should be used
     * @throws ClassCastException if the list contains elements that are not
     *         <i>mutually comparable</i> using the specified comparator
     * @throws UnsupportedOperationException if the list's list-iterator does
     *         not support the @code set operation
     * @throws IllegalArgumentException
     *         (<a href="Collection.html#optional-restrictions">optional</a>)
     *         if the comparator is found to violate the @link Comparator
     *         contract
     * @since 1.8
     */
    @SuppressWarnings("unchecked", "rawtypes")
    default void sort(Comparator<? super E> c) 
        Object[] a = this.toArray();
        Arrays.sort(a, (Comparator) c);
        ListIterator<E> i = this.listIterator();
        for (Object e : a) 
            i.next();
            i.set((E) e);
        
    

    /**
     * Removes all of the elements from this list (optional operation).
     * The list will be empty after this call returns.
     *
     * @throws UnsupportedOperationException if the <tt>clear</tt> operation
     *         is not supported by this list
     */
    void clear();


    // Comparison and hashing

    /**
     * Compares the specified object with this list for equality.  Returns
     * <tt>true</tt> if and only if the specified object is also a list, both
     * lists have the same size, and all corresponding pairs of elements in
     * the two lists are <i>equal</i>.  (Two elements <tt>e1</tt> and
     * <tt>e2</tt> are <i>equal</i> if <tt>(e1==null ? e2==null :
     * e1.equals(e2))</tt>.)  In other words, two lists are defined to be
     * equal if they contain the same elements in the same order.  This
     * definition ensures that the equals method works properly across
     * different implementations of the <tt>List</tt> interface.
     *
     * @param o the object to be compared for equality with this list
     * @return <tt>true</tt> if the specified object is equal to this list
     */
    boolean equals(Object o);

      tempMap.put("b", 2);
  tempMap.put("c", 3);
  // JDK1.4中
  // 遍历方法一 hashmap entrySet() 遍历
  System.out.println("方法一");
  Iterator it = tempMap.entrySet().iterator();
  while (it.hasNext()) {
   Map.Entry entry = (Map.Entry) it.next();
   Object key = entry.getKey();
   Object value = entry.getValue();
   System.out.println("key=" + key + " value=" + value);
  }
  System.out.println("");
  // JDK1.5中,应用新特性For-Each循环
  // 遍历方法二
  System.out.println("方法二");
  for (Map.Entry<String, Integer> entry : tempMap.entrySet()) {
   String key = entry.getKey().toString();
   String value = entry.getValue().toString();
   System.out.println("key=" + key + " value=" + value);
  }
  System.out.println("");

  // 遍历方法三 hashmap keySet() 遍历
  System.out.println("方法三");
  for (Iterator i = tempMap.keySet().iterator(); i.hasNext();) {
   Object obj = i.next();
   System.out.println(obj);// 循环输出key
   System.out.println("key=" + obj + " value=" + tempMap.get(obj));
  }
  for (Iterator i = tempMap.values().iterator(); i.hasNext();) {
   Object obj = i.next();
   System.out.println(obj);// 循环输出value
  }
  System.out.println("");

  // 遍历方法四 treemap keySet()遍历
  System.out.println("方法四");
  for (Object o : tempMap.keySet()) {
   System.out.println("key=" + o + " value=" + tempMap.get(o));
  }
  System.out.println("11111");

  // java如何遍历Map <String, ArrayList> map = new HashMap <String,
  // ArrayList>();
  System.out
    .println("java  遍历Map <String, ArrayList> map = new HashMap

<String, ArrayList>();");
  Map<String, ArrayList> map = new HashMap<String, ArrayList>();
  Set<String> keys = map.keySet();
  Iterator<String> iterator = keys.iterator();
  while (iterator.hasNext()) {
   String key = iterator.next();
   ArrayList arrayList = map.get(key);
   for (Object o : arrayList) {
    System.out.println(o + "遍历过程");
   }
  }
  System.out.println("2222");
  Map<String, List> mapList = new HashMap<String, List>();
  for (Map.Entry entry : mapList.entrySet()) {
   String key = entry.getKey().toString();
   List<String> values = (List) entry.getValue();
   for (String value : values) {
    System.out.println(key + " --> " + value);
   }
  }
 }
}

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