Summary
-------

Clarify the "default charset" in several locations of `java.lang.String` class documentation.

Problem
-------

There are locations that read "platform's default charset." Users would be confused it would mean the `native.encoding` which was the case before JEP 400, but now it is `UTF-8`.

Solution
--------

Clarify the phrase "platform's default charset" in `java.lang.String` class and methods descriptions, by replacing it with a link to `java.nio.charset.Charset#defaultCharset()` so that  the definition of  "default charset" is clearly understood.

Specification
-------------

    diff a/src/java.base/share/classes/java/lang/String.java b/src/java.base/share/classes/java/lang/String.java
    --- a/src/java.base/share/classes/java/lang/String.java
    +++ b/src/java.base/share/classes/java/lang/String.java
    @@ -364,13 +364,12 @@
          * <p> Each {@code byte} in the subarray is converted to a {@code char} as
          * specified in the {@link #String(byte[],int) String(byte[],int)} constructor.
          *
          * @deprecated This method does not properly convert bytes into characters.
          * As of JDK&nbsp;1.1, the preferred way to do this is via the
    -     * {@code String} constructors that take a {@link
    -     * java.nio.charset.Charset}, charset name, or that use the platform's
    -     * default charset.
    +     * {@code String} constructors that take a {@link Charset}, charset name,
    +     * or that use the {@link Charset#defaultCharset() default charset}.
          *
          * @param  ascii
          *         The bytes to be converted to characters
          *
          * @param  hibyte
    @@ -426,13 +425,12 @@
          *                         | (<b><i>b</i></b> &amp; 0xff))
          * </pre></blockquote>
          *
          * @deprecated  This method does not properly convert bytes into
          * characters.  As of JDK&nbsp;1.1, the preferred way to do this is via the
    -     * {@code String} constructors that take a {@link
    -     * java.nio.charset.Charset}, charset name, or that use the platform's
    -     * default charset.
    +     * {@code String} constructors that take a {@link Charset}, charset name,
    +     * or that use the {@link Charset#defaultCharset() default charset}.
          *
          * @param  ascii
          *         The bytes to be converted to characters
          *
          * @param  hibyte
    @@ -1383,13 +1381,13 @@
             this(bytes, 0, bytes.length, charset);
         }
     
         /**
          * Constructs a new {@code String} by decoding the specified subarray of
    -     * bytes using the platform's default charset.  The length of the new
    -     * {@code String} is a function of the charset, and hence may not be equal
    -     * to the length of the subarray.
    +     * bytes using the {@link Charset#defaultCharset() default charset}.
    +     * The length of the new {@code String} is a function of the charset,
    +     * and hence may not be equal to the length of the subarray.
          *
          * <p> The behavior of this constructor when the given bytes are not valid
          * in the default charset is unspecified.  The {@link
          * java.nio.charset.CharsetDecoder} class should be used when more control
          * over the decoding process is required.
    @@ -1413,13 +1411,13 @@
             this(bytes, offset, length, Charset.defaultCharset());
         }
     
         /**
          * Constructs a new {@code String} by decoding the specified array of bytes
    -     * using the platform's default charset.  The length of the new {@code
    -     * String} is a function of the charset, and hence may not be equal to the
    -     * length of the byte array.
    +     * using the {@link Charset#defaultCharset() default charset}. The length
    +     * of the new {@code String} is a function of the charset, and hence may not
    +     * be equal to the length of the byte array.
          *
          * <p> The behavior of this constructor when the given bytes are not valid
          * in the default charset is unspecified.  The {@link
          * java.nio.charset.CharsetDecoder} class should be used when more control
          * over the decoding process is required.
    @@ -1691,11 +1689,12 @@
          *     dstBegin + (srcEnd-srcBegin) - 1
          * </pre></blockquote>
          *
          * @deprecated  This method does not properly convert characters into
          * bytes.  As of JDK&nbsp;1.1, the preferred way to do this is via the
    -     * {@link #getBytes()} method, which uses the platform's default charset.
    +     * {@link #getBytes()} method, which uses the {@link Charset#defaultCharset()
    +     * default charset}.
          *
          * @param  srcBegin
          *         Index of the first character in the string to copy
          *
          * @param  srcEnd
    @@ -1778,11 +1777,12 @@
             return encode(charset, coder(), value);
          }
     
         /**
          * Encodes this {@code String} into a sequence of bytes using the
    -     * platform's default charset, storing the result into a new byte array.
    +     * {@link Charset#defaultCharset() default charset}, storing the result
    +     * into a new byte array.
          *
          * <p> The behavior of this method when this string cannot be encoded in
          * the default charset is unspecified.  The {@link
          * java.nio.charset.CharsetEncoder} class should be used when more control
          * over the encoding process is required.