1、找到java的安裝路徑，我拿我自己的安裝路徑舉例：
2、我想查找String類的使用方法，首先你要知道String所屬包名，String是java.lang.String，一下是查看幫助文檔的路徑：

C:\Program Files\Java\jdk1.7.0_67\src.zip\java\lang\String.java

找到注釋：

/*** The <code>String</code> class represents character strings. All* string literals in Java programs, such as <code>"abc"</code>, 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:* <p><blockquote><pre>* String str = "abc";* </pre></blockquote><p>* is equivalent to:* <p><blockquote><pre>* char data[] = {'a', 'b', 'c'};* String str = new String(data);* </pre></blockquote><p>* Here are some more examples of how strings can be used:* <p><blockquote><pre>* System.out.println("abc");* String cde = "cde";* System.out.println("abc" + cde);* String c = "abc".substring(2,3);* String d = cde.substring(1, 2);* </pre></blockquote>* <p>* The class <code>String</code> 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.* <p>* 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</code>(or <code>StringBuffer</code>)* class and its <code>append</code> method.* String conversions are implemented through the method* <code>toString</code>, defined by <code>Object</code> 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>.** <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.** <p>A <code>String</code> represents a string in the UTF-16 format* in which <em>supplementary characters</em> are represented by <em>surrogate* pairs</em> (see the section <a href="Character.html#unicode">Unicode* Character Representations</a> in the <code>Character</code> class for* more information).* Index values refer to <code>char</code> code units, so a supplementary* character uses two positions in a <code>String</code>.* <p>The <code>String</code> class provides methods for dealing with* Unicode code points (i.e., characters), in addition to those for* dealing with Unicode code units (i.e., <code>char</code> values).** @author Lee Boynton* @author Arthur van Hoff* @author Martin Buchholz* @author Ulf Zibis* @see java.lang.Object#toString()* @see java.lang.StringBuffer* @see java.lang.StringBuilder* @see java.nio.charset.Charset* @since JDK1.0*/

好啦，這就是java的幫助文檔…英語不好的童鞋可以使用有道翻譯哦~

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