Java String 翻译

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本文深入探讨 Java 中 String 类的基本概念、特性、如何在代码中使用字符串以及常用的操作方法，包括字符串的连接、转换、比较、提取子串等功能，并解释了字符串的不可变性、字符编码及 Unicode 标准。通过具体实例，帮助开发者掌握 Java 字符串处理的核心技巧。

The String class represents (表示，描述 ) character strings. All string literals in Java programs, such (例如 ) as "abc" , are implemented as instances of this class.

Strings are constant (常量 ); their values cannot be changed after they are created. String buffers (缓冲 ) support mutable (可变 ) strings. Because String objects are immutable (不可变 ) they can be shared. For example:

     String str = "abc";

is equivalent (等值的 ) to:

     char data[] = {'a', 'b', 'c'};
     String str = new String(data);

Here are some more examples of how strings can be used:

     System.out.println("abc");
     String cde = "cde";
     System.out.println("abc" + cde);
     String c = "abc".substring(2,3);
     String d = cde.substring(1, 2);

The class String includes methods for examining (检查 ) individual (个体 ) characters of the sequence, for comparing (比较 ) strings, for searching strings, for extracting (提起 ) 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 (标准 ) version specified by the Character class.

The Java language provides (提供 ) special (特别 ) support for the string concatenation (连接 ) operator ( + ), and for conversion of other objects to strings. String concatenation is implemented through the StringBuilder (or StringBuffer ) class and its append method. String conversions are implemented through the method toString , defined by Object and inherited (继承 ) by all classes in Java. For additional (额外的 ) information on string concatenation and conversion, see Gosling, Joy, and Steele, The Java Language Specification .

Unless (除非 ) otherwise (另外 ) noted, passing a null argument to a constructor or method in this class will cause (引起 ) a NullPointerException to be thrown.

A String represents a string in the UTF-16 format in which supplementary (增补 ) characters are represented by surrogate pairs (see the section Unicode Character Representations in the Character class for more information). Index values refer (指 ) to char code units (单元，单位 ), so a supplementary character uses two positions in a String .

The String class provides methods for dealing with Unicode code points (i.e., characters), in addition (添加 ) to those for dealing (行为 ) with Unicode code units (i.e., char values).