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Java-Enumeration interface summary details

黄舟

Release： 2017-03-15 11:52:01

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What you learn on paper is shallow, but you know you have to do it in detail --Lu You Ask the canal how clear it is so that there is a source of living water --Zhu Xi

Enumeration ( Enumeration) Interface has a similar function to Iterator. It only provides the function of traversing the elements of Vector and HashTable type collections, and does not support the removal operation of elements.

The source code of the Enumeration interface in Java8:

public interface Enumeration<E> {
/**
     * Tests if this enumeration contains more elements.
     *
     * @return  <code>true</code> if and only if this enumeration object
     *           contains at least one more element to provide;
     *          <code>false</code> otherwise.
     */
boolean hasMoreElements();//判断是否包含元素

/**
     * Returns the next element of this enumeration if this enumeration
     * object has at least one more element to provide.
     *
     * @return     the next element of this enumeration.
     * @exception  NoSuchElementException  if no more elements exist.
     */
E nextElement();//获得下一个元素
}

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According to the source code analysis of Enumeration, Enumeration has two methods:

(1) boolean hasMoreElements();// Whether there are still elements, if so, return true, otherwise it means that it contains at least one element

(2)E nextElement();//If the Enumeration enumeration object still has elements, the returned object is only The next element that can be found, otherwise a NoSuchElementException is thrown.

Simple example:

public class TestEnumeration{
public static void main(String[] args){
        Vector v = new Vector();
        v.addElement("Lisa");
        v.addElement("Billy");
        v.addElement("Mr Brown");
        Enumeration e = v.elements();//返回Enumeration对象
        while(e.hasMoreElements()){
            String value = (String)e.nextElement();//调用nextElement方法获得元素
            System.out.print(value);
        }
    }
}

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