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java charsequence是什麼，讓我們一起了解一下？
CharSequence類是java.lang包下的一個接口，此接口對多種不同的對char訪問的統一接口，像String、StringBuffer、StringBuilder類都是CharSequence的子接口。
那麼CharSequence接口是如何實現的？
CharSequence接口的源碼如下：
package java.lang;/** * A <tt>CharSequence</tt> is a readable sequence of <code>char</code> values. This * interface provides uniform, read-only access to many different kinds of * <code>char</code> sequences. * A <code>char</code> value represents a character in the <i>Basic * Multilingual Plane (BMP)</i> or a surrogate. Refer to <a * href="Character.html#unicode">Unicode Character Representation</a> for details. * * <p> This interface does not refine the general contracts of the {@link * java.lang.Object#equals(java.lang.Object) equals} and {@link * java.lang.Object#hashCode() hashCode} methods. The result of comparing two * objects that implement <tt>CharSequence</tt> is therefore, in general, * undefined. Each object may be implemented by a different class, and there * is no guarantee that each class will be capable of testing its instances * for equality with those of the other. It is therefore inappropriate to use * arbitrary <tt>CharSequence</tt> instances as elements in a set or as keys in * a map. </p> * * @author Mike McCloskey * @since 1.4 * @spec JSR-51 */public interface CharSequence { /** * Returns the length of this character sequence. The length is the number * of 16-bit <code>char</code>s in the sequence.</p> * * @return the number of <code>char</code>s in this sequence */ int length(); /** * Returns the <code>char</code> value at the specified index. An index ranges from zero * to <tt>length() - 1</tt>. The first <code>char</code> value of the sequence is at * index zero, the next at index one, and so on, as for array * indexing. </p> * * <p>If the <code>char</code> value specified by the index is a * <a href="{@docRoot}/java/lang/Character.html#unicode">surrogate</a>, the surrogate * value is returned. * * @param index the index of the <code>char</code> value to be returned * * @return the specified <code>char</code> value * * @throws IndexOutOfBoundsException * if the <tt>index</tt> argument is negative or not less than * <tt>length()</tt> */ char charAt(int index); /** * Returns a new <code>CharSequence</code> that is a subsequence of this sequence. * The subsequence starts with the <code>char</code> value at the specified index and * ends with the <code>char</code> value at index <tt>end - 1</tt>. The length * (in <code>char</code>s) of the * returned sequence is <tt>end - start</tt>, so if <tt>start == end</tt> * then an empty sequence is returned. </p> * * @param start the start index, inclusive * @param end the end index, exclusive * * @return the specified subsequence * * @throws IndexOutOfBoundsException * if <tt>start</tt> or <tt>end</tt> are negative, * if <tt>end</tt> is greater than <tt>length()</tt>, * or if <tt>start</tt> is greater than <tt>end</tt> */ CharSequence subSequence(int start, int end); /** * Returns a string containing the characters in this sequence in the same * order as this sequence. The length of the string will be the length of * this sequence. </p> * * @return a string consisting of exactly this sequence of characters */ public String toString();}
另外CharSequence類是一個描述字符串的一個描述型接口，有三個類實現了該接口，分別為：String、StringBuffer、StringBuilder類，所以説，看到這個類，就直接當做是一個字符串類型就可以了，示例代碼如下：
/** * String、Stringbuffer、StringBuilder 三個字符相關的類都實現 * 了CharSequence 類，所以説，以後見到CharSequence描述的就是字符串 */ public class CharSequenceStudy { public static void main(String[] args) { CharSequence str = "www.ayit.com"; CharSequence sub = str.subSequence(4,8); System.out.println(sub); System.out.println(str.length()); }}拓展一下：對於抽象類或者接口來説不可以直接使用new的方式創建對象，但是可以直接給它賦值； CharSequence b = "s"; > 。CharSequence b = "s" 是一個類型強轉操作，等於CharSequence b = (CharSequence) new String("s")。
