java基础源码 (1)--String类

这个是String类上面的注释，我用谷歌翻译翻译的，虽然有点语法上的问题，但是大概都可以翻译出来

/**
 * 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}类表示字符串。所有java程序中的字符文字，例如{@code "abc"}，是作为此类的实例实现。

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:

字符串是不变的；他们的价值观无法改变已创建（这句话的意思我个人觉得应该是：已经创建就无法修改）。
字符串缓冲区支持可变字符串。因为String对象是不可变的。所以可以共享他们。

* 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.

类{@code String}包括检查方法
 *序列的各个字符，用于比较字符串
 *搜索字符串，提取子字符串，以及创建
 *一个字符串的副本，所有字符都翻译成大写或
 *小写。案例映射基于Unicode标准版本
 *由{@link java.lang.Character Character}类指定。

介绍了String类里面包括的一些内容（检查方法，序列的各个字符，比较字符串，搜索字符串，
* 提取子字符串，创建一个字符串的副本，所有字符翻译大，小写，）

 *  * The Java language provides special support for the string
 * concatenation operator ( + ), 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的转换是通过由java中的所有类继承的Object里面定义的toString()方法实现
 * 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语言为字符串提供特殊支持
 *连接运算符（＆nbsp; +＆nbsp;），用于转换
 *其他对象到字符串。字符串连接已实现
 *通过{@code StringBuilder}（或{@code StringBuffer}）
 *类及其{@code append}方法。
 *字符串转换通过该方法实现
 * {@code toString}，由{@code Object}定义
 *由Java中的所有类继承。有关其他信息
 *字符串连接和转换，请参阅Gosling，Joy和Steele，
 * <i> Java语言规范</ i>。
＆nbsp;代表不换行空格的意思

 * <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.

除非另有说明，否者将NULL参数传递给构造函数或此类中的方法将导致NullPointerException（空指针异常）

现在开始学习：

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

首先他是final类型的，是不可修改，然后实现了Serializable，Comparable，CharSequence这个3个接口

Serializable：这个是Serializablelei类源码上的注释

* 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. 

　翻译的大概意思是,类的序列化是由java.io.Serializable接口的类启用。不实现此接口的类将不会使用任何状态序列化或反序列化，可序列化的所有子类型都是可序列化的，序列化接口没有方法或字段，仅用于标识可串行话的语义。

Comparable:

　　JDK1.8文档的意思是该接口对实现它的每个类的对象加强一个整体排序。这个排序被称为类的自然排序，类的compareTo方法被称为自然比较方法。

　　例子（借鉴别人的）

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) {
        /*
        * 比较此对象与指定对象的顺序，如果对象小于
        * 等于或大于指定对象，则分别返回整数，零，或负数
        * */
        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("科纪", 21);
        Persion persion3 = new Persion("伟克", 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("排序之后........................");

    }

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值的可读序列，该界面提供统一的，只读访问许多不同类型的char序列，char值代表基本多语言平面（BMP）或者代理中的一个字符

* * <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 */
此界面不会完善equals和hashCode方法的一般合同。因此，比较两个对象实现CharSequence其结果是，一般情况下，不确定的，每个对象可以由不同的类实现，并且不能保证每个类都能够测试其实例以与另一个类相同，因此，使用任意的CharSequence
实例作为集合中的元素或映射中的键是不合适的。

 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.
 *返回此字符序列的长度，这个数字序列是长度为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指定索引处的值。索引范围从0到length()-1.序列的第一个char值在索引为零，下一个索引为1，
以此类推，就像数组索引一样
 * <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，则返回所述替代值
 * <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
 *参数 index,要返回的char值的索引
 * @return  the specified <code>char</code> value
 *返回        指定值为char
 * @throws  IndexOutOfBoundsException
 *          if the <tt>index</tt> argument is negative or not less than
 *          <tt>length()</tt>
　　异常 IndexOutOfBuoundsException 如果index参数为负数或不低于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.
 *　返回一个CharSequence，这是这个序列的一个子序列。子char以指定索引的char值开始，以索引end-1的char
值结束，返回序列的长度（chars）为end-start,因此如果start==end则返回一个空序列
 * @param   start   the start index, inclusive
　　参数     start    包含起始索引
 * @param   end     the end index, exclusive
 * 参数      end     结束索引，独占
 * @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>
 */异常   indexOutOfBoundsException 如果start或end为负数，如果end大于length（）
　　　　　　，或者如果start大于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.
 *以与此顺序相同的顺序返回包含此序列中的字符的字符串，字符串的长度将是此序列的长度
 * @return  a string consisting of exactly this sequence of characters
 */ 返回      一个由这个字符序列组成的字符串
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，从这个序列零扩展char值，映射到surrogate code point的任何字符通过未
解释的方式传递
 * <p>If the sequence is mutated while the stream is being read, the
 * result is undefined.
 *如果序列在流被读取时被突变，则结果是未定义的

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