java基礎源碼 (1)--String類

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這個是String類上面的注釋，我用Google翻譯翻譯的，雖然有點文法上的問題，但是大概都可以翻譯出來

 

/** * The {@code String} class represents character strings. All * string literals in Java programs, such as {@code "abc"}, are * implemented as instances of this class. * <p> * Strings are constant; their values cannot be changed after they * are created. String buffers support mutable strings. * Because String objects are immutable they can be shared. For example:

{@code String}類表示字串。所有java程式中的字元文字，例如{@code "abc"}，是作為此類的執行個體實現。

The {@code String} class represents character strings. All * string literals in Java programs, such as {@code "abc"}, are * implemented as instances of this class. * <p> * Strings are constant; their values cannot be changed after they * are created. String buffers support mutable strings. * Because String objects are immutable they can be shared. For example:

字串是不變的；他們的價值觀無法改變已建立（這句話的意思我個人覺得應該是：已經建立就無法修改）。
字串緩衝區支援可變字串。因為String對象是不可變的。所以可以共用他們。

* The class {@code String} includes methods for examining * individual characters of the sequence, for comparing strings, for * searching strings, for extracting substrings, and for creating a * copy of a string with all characters translated to uppercase or to * lowercase. Case mapping is based on the Unicode Standard version * specified by the {@link java.lang.Character Character} class.

類{@code String}包括檢查方法
 *序列的各個字元，用於比較字串
 *搜尋字串，提取子字串，以及建立
 *一個字串的副本，所有字元都翻譯成大寫或
 *小寫。案例映射基於Unicode標準版本
 *由{@link java.lang.Character Character}類指定。

介紹了String類裡麵包括的一些內容（檢查方法，序列的各個字元，比較字串，搜尋字串，
* 提取子字串，建立一個字串的副本，所有字元翻譯大，小寫，）

 *  * The Java language provides special support for the string * concatenation operator (&nbsp;+&nbsp;), and for conversion of * other objects to strings. String concatenation is implemented * through the {@code StringBuilder}(or {@code StringBuffer}) * class and its {@code append} method. * String的轉換是通過由java中的所有類繼承的Object裡面定義的toString()方法實現 * String conversions are implemented through the method * {@code toString}, defined by {@code Object} and * inherited by all classes in Java. For additional information on * string concatenation and conversion, see Gosling, Joy, and Steele, *  * <i>The Java Language Specification</i>. *   * Java語言為字串提供特殊支援 *串連運算子（＆nbsp; +＆nbsp;），用於轉換 *其他對象到字串。字串串連已實現 *通過{@code StringBuilder}（或{@code StringBuffer}） *類及其{@code append}方法。 *字串轉換通過該方法實現 * {@code toString}，由{@code Object}定義 *由Java中的所有類繼承。有關其他資訊 *字串串連和轉換，請參閱Gosling，Joy和Steele， * <i> Java語言規範</ i>。＆nbsp;代表不換行空格的意思

 * <p> Unless otherwise noted, passing a <tt>null</tt> argument to a constructor * or method in this class will cause a {@link NullPointerException} to be * thrown.

除非另有說明，否者將NULL參數傳遞給建構函式或此類中的方法將導致NullPointerException（null 指標異常）

現在開始學習：

public final class String implements java.io.Serializable, Comparable<String>, CharSequence {

首先他是final類型的，是不可修改，然後實現了Serializable，Comparable，CharSequence這個3個介面

Serializable：這個是Serializablelei類源碼上的注釋

* Serializability of a class is enabled by the class implementing the * java.io.Serializable interface. Classes that do not implement this * interface will not have any of their state serialized or * deserialized.  All subtypes of a serializable class are themselves * serializable.  The serialization interface has no methods or fields * and serves only to identify the semantics of being serializable. 

　翻譯的大概意思是,類的序列化是由java.io.Serializable介面的類啟用。不實現此介面的類將不會使用任何狀態序列化或還原序列化，可序列化的所有子類型都是可序列化的，序列化介面沒有方法或欄位，僅用於標識可串列話的語義。

Comparable:

　　JDK1.8文檔的意思是該介面對實現它的每個類的對象加強一個整體排序。這個排序被稱為類的自然排序，類的compareTo方法被稱為自然比較方法。

　　例子（借鑒別人的）

public class Persion implements Comparable<Persion> {     String name;     int age;    public Persion(String name, int age) {        this.name = name;        this.age = age;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public int getAge() {        return age;    }    public void setAge(int age) {        this.age = age;    }    public int compareTo(Persion o) {        /*        * 比較此對象與指定對象的順序，如果對象小於        * 等於或大於指定對象，則分別返回整數，零，或負數        * */        return compare(this.age,o.age);    }    public static int compare(long age1,long age2){        return (age1>age2?1:(age1==age2?0:-1));    }    @Override    public String toString() {        return "Persion{" +                "name=‘" + name + ‘\‘‘ +                ", age=" + age +                ‘}‘;    }}   public static void main(String[] args){        Persion persion2 = new Persion("世界", 23);        Persion persion1 = new Persion("科紀", 21);        Persion persion3 = new Persion("偉克", 25);        List<Persion>persionList=new ArrayList<Persion>();        persionList.add(persion2);        persionList.add(persion1);        persionList.add(persion3);        for (Persion person1 : persionList) {            System.out.println(person1.toString());        }        System.out.println("排序之前........................");        Collections.sort(persionList);        for (Persion person1 : persionList) {            System.out.println(person1.toString());        }        System.out.println("排序之後........................");    }

 CharSequence：

　　 

/** * 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.
　　CharSequence是char值的可讀序列，該介面提供統一的，唯讀訪問許多不同類型的char序列，char值代表基本多語言平面（BMP）或者代理中的一個字元

* * <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 */
此介面不會完善equals和hashCode方法的一般合約。因此，比較兩個對象實現CharSequence其結果是，一般情況下，不確定的，每個對象可以由不同的類實現，並且不能保證每個類都能夠測試其執行個體以與另一個類相同，因此，使用任意的CharSequence
執行個體作為集合中的元素或映射中的鍵是不合適的。

 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.
 *返回此字元序列的長度，這個數字序列是長度為16位char的

 * @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.
 *返回char指定索引處的值。索引範圍從0到length()-1.序列的第一個char值在索引為零，下一個索引為1，
以此類推，就像數組索引一樣
 * <p>If the <code>char</code> value specified by the index is a
如果char由索引指定的值是surrogate，則返回所述替代值
 * <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
 *參數 index,要返回的char值的索引
 * @return  the specified <code>char</code> value
 *返回        指定值為char
 * @throws  IndexOutOfBoundsException
 *          if the <tt>index</tt> argument is negative or not less than
 *          <tt>length()</tt>
　　異常 IndexOutOfBuoundsException 如果index參數為負數或不低於length()
 */
char charAt(int index);

 * Returns a <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.
 *　返回一個CharSequence，這是這個序列的一個子序列。子char以指定索引的char值開始，以索引end-1的char
值結束，返回序列的長度（chars）為end-start,因此如果start==end則返回一個空序列
 * @param   start   the start index, inclusive
　　參數     start    包含起始索引
 * @param   end     the end index, exclusive
 * 參數      end     結束索引，獨佔
 * @return  the specified subsequence
　　返回       指定的子序列
 *
 * @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>
 */異常   indexOutOfBoundsException 如果start或end為負數，如果end大於length（）
　　　　　　，或者如果start大於end
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.
 *以與此順序相同的順序返回包含此序列中的字元的字串，字串的長度將是此序列的長度
 * @return  a string consisting of exactly this sequence of characters
 */ 返回      一個由這個字元序列組成的字串
public String toString();

 * Returns a stream of {@code int} zero-extending the {@code char} values
 * from this sequence.  Any char which maps to a <a
 * href="{@docRoot}/java/lang/Character.html#unicode">surrogate code
 * point</a> is passed through uninterpreted.
 *　返回Int的流，從這個序列零擴充char值，映射到surrogate code point的任何字元通過未
解釋的方式傳遞
 * <p>If the sequence is mutated while the stream is being read, the
 * result is undefined.
 *如果序列在流被讀取時被突變，則結果是未定義的

 * @return an IntStream of char values from this sequence
　　返回     這個序列中的char值的intStream
 * @since 1.8
 */
public default IntStream chars() {

java基礎源碼 (1)--String類