Java中表示字符串的有三个类：String、StringBuffer和StringBuilder。其中，String的长度是不可变的，而StringBuffer和StringBuilder是长度可变的。对于StringBuffer和StringBuilder来说，两者的API几乎一模一样，因为两者有共同的父类：AbstractStringBuilder。区别在于StringBuffer的大部分方法都是被synchronized关键字修饰，是线程安全的，而StringBuilder则与其相反。
所以本篇就对StringBuffer和StringBuilder类比着来进行介绍。
- 构造器
StringBuffer和StringBuilder的构造器都有三个，分别如下：
StringBuffer的构造器：
- new StringBuffer(int capacity)
- new StringBuffer(String str)
- new StringBuffer(CharSequence seq)
StringBuilder的构造器：
- new StringBuilder(int capacity)
- new StringBuilder(String str)
- new StringBuilder(CharSequence seq)
对比两者构造器发现，它们对构造器的重载都施行了同样的方式，可以传入一个整数的容量，可以传一个字符串值，甚至可以传一个字符序列的对象。对于Java来说，常用的字符序列对象就是我们认知中的String， StringBuffer和StringBuilder。关于StringBuilder和StringBuffer的使用的示例代码如下所示：
<code>public
class
StringTest
{public
static
void
main
(String[] args
) throws IOException { StringBuffer strBuffer =new
StringBuffer(16
); System.out
.println("strBuffer："
+ strBuffer +", 容量为："
+ strBuffer.capacity() +", 长度为："
+ strBuffer.length()); StringBuilder strBuilder =new
StringBuilder(16
); System.out
.println("strBuilder："
+ strBuilder +", 容量为："
+ strBuilder.capacity() +", 长度为："
+ strBuilder.length()); StringBuffer strBuffer2 =new
StringBuffer("how are you"
); System.out
.println("strBuffer2的值为："
+ strBuffer2 +", 容量为："
+ strBuffer2.capacity() +", 长度为："
+ strBuffer2.length()); StringBuilder strBuilder2 =new
StringBuilder("how old are you"
); System.out
.println("strBuilder2的值为："
+ strBuilder2 +", 容量为："
+ strBuilder2.capacity() +", 长度为："
+ strBuilder2.length()); StringBuilder strBuffer3 =new
StringBuilder(strBuilder); System.out
.println("strBuffer3的值为："
+ strBuffer3 +", 容量为："
+ strBuffer3.capacity() +", 长度为："
+ strBuffer3.length()); StringBuilder strBuilder3 =new
StringBuilder(strBuffer2); System.out
.println("strBuilder3的值为："
+ strBuilder3 +", 容量为："
+ strBuilder3.capacity() +", 长度为："
+ strBuilder3.length()); } }/<code>
执行结果如下图所示：
- 拼接参数
拼接参数常用的方法方法如下图：
也就是说，该方法可以拼接所有的基本数据类型和其对应的包装类型，字符数组、字符序列对象及其他的引用对象等。
StringBuilder和StringBuffer的append
其示例代码如下所示：
<code>public class StringTest {
public static void main(String[] args) throws IOException {
StringBuilder strBuilder = new
StringBuilder();
StringBuffer strBuffer = new
StringBuffer();
strBuilder.append
(12
).append
(","
);
strBuffer.append
(12
).append
(","
);
strBuilder.append
(13
L).append
(","
);
strBuffer.append
(13
L).append
(","
);
strBuilder.append
(3.4
f).append
(","
);
strBuffer.append
(3.4
f).append
(","
);
strBuilder.append
(3.5
).append
(","
);
strBuffer.append
(3.5
).append
(","
);
strBuilder.append
("hello"
.toCharArray()).append
(","
);
strBuffer.append
("hello"
.toCharArray()).append
(","
);
strBuilder.append
(new
Date()).append
(","
);
strBuffer.append
(new
Date()).append
(","
);
strBuilder.append
("hello"
.toCharArray(), 2
, 2
).append
(","
);
strBuffer.append
("hello"
.toCharArray(), 2
, 2
).append
(","
);
strBuilder.append
("hello"
, 1
, 3
).append
(","
);
strBuffer.append
("hello"
, 1
, 3
).append
(","
);
printStrBuilder(strBuilder);
printStrBuffer(strBuffer);
}
private static void printStrBuilder(StringBuilder strBuilder) {
String[] strArr = strBuilder.deleteCharAt(strBuilder.length() - 1
).toString().split(","
);
System.out.println
("StringBuilder信息为：\n"
+ Arrays.asList(strArr));
}
private static void printStrBuffer(StringBuffer strBuffer) {
String[] strArr = strBuffer.deleteCharAt(strBuffer.length() - 1
).toString().split(","
);
System.out.println
("StringBuffer信息为：\n"
+ Arrays.asList(strArr));
}
}
/<code>只想结果如下图所示：
- 获取某个字符串在另一个字符串中的索引位置
这里使用的方法有四个，如下图：
相关的示例代码如下所示：
<code>public
class
StringTest
{public
static
void
main
(String[] args
) throws IOException { StringBuilder strBuilder =new
StringBuilder("no zuo no die no happy no problem"
); StringBuffer strBuffer =new
StringBuffer("no zuo no die no happy no problem"
); System.out
.println(""no"在strBuilder中首次出现的位置为："
+ strBuilder.indexOf("no"
)); System.out
.println(""no"在strBuffer中首次出现的位置为："
+ strBuffer.indexOf("no"
)); System.out
.println(""no"在strBuilder中在索引3之后首次出现的位置为："
+ strBuilder.indexOf("no"
,3
)); System.out
.println(""no"在strBuffer中在索引3之后首次出现的位置为："
+ strBuffer.indexOf("no"
,3
)); System.out
.println(""no"在strBuilder中最后出现的位置为："
+ strBuilder.lastIndexOf("no"
)); System.out
.println(""no"在strBuffer中最后出现的位置为："
+ strBuffer.lastIndexOf("no"
)); System.out
.println(""no"在strBuilder中在索引20之前最后出现的位置为："
+ strBuilder.lastIndexOf("no"
,20
)); System.out
.println(""no"在strBuffer中在索引20之前最后出现的位置为："
+ strBuffer.lastIndexOf("no"
,20
)); } } /<code>
执行结果如下图所示：
- 插入方法
插入方法为：insert(int offset, XXX xxx）, 目的是在偏移offset个字符后插入xxx。这里的xxx表示所有的基本数据类型及其对应的包装类型、字符数组、字符序列对象和其他的引用对象等。常用方法如下：
相关示例代码如下所示：
<code>public
class
StringTest
{public
static
void
main
(String[] args
) { StringBuilder strBuilder =new
StringBuilder("hello"
); StringBuffer strBuffer =new
StringBuffer("hello"
); System.out
.println("在strBuilder偏移2位后插入整数3的结果为："
+ strBuilder.insert(2
,3
)); System.out
.println("在strBuffer偏移3位后插入整数3的结果为："
+ strBuffer.insert(3
,3
)); StringBuilder strBuilder2 =new
StringBuilder("world"
); StringBuffer strBuffer2 =new
StringBuffer("world"
); System.out
.println("在strBuilder2偏移2位后插入'好'的结果为："
+ strBuilder2.insert(2
,'好'
)); System.out
.println("在strBuffer2偏移3位后插入'好'的结果为："
+ strBuffer2.insert(3
,'好'
)); StringBuilder strBuilder3 =new
StringBuilder("what"
); StringBuffer strBuffer3 =new
StringBuffer("what"
); System.out
.println("在strBuilder3偏移2位后插入4L的结果为："
+ strBuilder3.insert(2
,4L
)); System.out
.println("在strBuffer3偏移3位后插入4L的结果为："
+ strBuffer3.insert(3
,4L
)); StringBuilder strBuilder4 =new
StringBuilder("where"
); StringBuffer strBuffer4 =new
StringBuffer("where"
); System.out
.println("在strBuilder4偏移2位后插入3.14F的结果为："
+ strBuilder4.insert(2
,3.14F
)); System.out
.println("在strBuffer4偏移3位后插入3.14F的结果为："
+ strBuffer4.insert(3
,3.14F
)); StringBuilder strBuilder5 =new
StringBuilder("when"
); StringBuffer strBuffer5 =new
StringBuffer("when"
); System.out
.println("在strBuilder5偏移2位后插入1.414的结果为："
+ strBuilder5.insert(2
,1.414
)); System.out
.println("在strBuffer5偏移3位后插入1.414的结果为："
+ strBuffer5.insert(3
,1.414
)); StringBuilder strBuilder6 =new
StringBuilder("crazy"
); StringBuffer strBuffer6 =new
StringBuffer("crazy"
); System.out
.println("在strBuilder6偏移2位后插入true的结果为："
+ strBuilder6.insert(2
,true
)); System.out
.println("在strBuffer6偏移3位后插入false的结果为："
+ strBuffer6.insert(3
,false
)); StringBuilder strBuilder7 =new
StringBuilder("hehe"
); StringBuffer strBuffer7 =new
StringBuffer("hehe"
); System.out
.println("在strBuilder7偏移2位后插入Date的结果为："
+ strBuilder7.insert(2
,new
Date())); System.out
.println("在strBuffer7偏移3位后插入Date的结果为："
+ strBuffer7.insert(3
,new
Date())); StringBuilder strBuilder8 =new
StringBuilder("this"
); StringBuffer strBuffer8 =new
StringBuffer("this"
); System.out
.println("在strBuilder8偏移2位后插入字符数组['a', 'r', 'e']的结果为："
+ strBuilder8.insert(2
,new
char
[]{'a'
,'r'
,'e'
})); System.out
.println("在strBuffer8偏移3位后插入字符数组['a', 'r', 'e']的结果为："
+ strBuffer8.insert(3
,new
char
[]{'a'
,'r'
,'e'
})); StringBuilder strBuilder9 =new
StringBuilder("happend"
); StringBuffer strBuffer9 =new
StringBuffer("happend"
); System.out
.println("在strBuilder9偏移2位后插入Date的结果为："
+ strBuilder9.insert(2
,new
StringBuffer("234"
))); System.out
.println("在strBuffer9偏移3位后插入Date的结果为："
+ strBuffer9.insert(3
,new
StringBuilder("234"
))); StringBuilder strBuilder10 =new
StringBuilder("that"
); StringBuffer strBuffer10 =new
StringBuffer("that"
); System.out
.println("在strBuilder10偏移2位后插入字符数组['a', 'r', 'e']的结果为："
+ strBuilder10.insert(2
,new
char
[]{'a'
,'r'
,'e'
},0
,2
)); System.out
.println("在strBuffer10偏移3位后插入字符数组['a', 'r', 'e']的结果为："
+ strBuffer10.insert(3
,new
char
[]{'a'
,'r'
,'e'
},0
,2
)); StringBuilder strBuilder11 =new
StringBuilder("jerry"
); StringBuffer strBuffer11 =new
StringBuffer("jerry"
); System.out
.println("在strBuilder11偏移2位后插入Date的结果为："
+ strBuilder11.insert(2
,new
StringBuffer("234"
),0
,2
)); System.out
.println("在strBuffer11偏移3位后插入Date的结果为："
+ strBuffer11.insert(3
,new
StringBuilder("234"
),0
,2
)); } }/<code>
执行结果如下图所示：
- 删除某个或某些字符
删除某个或某些的字符方法如下图所示：
相关示例代码如下：
<code>public
class
StringTest
{public
static
void
main
(String[] args
) { StringBuilder strBuilder =new
StringBuilder("hello"
); StringBuffer strBuffer =new
StringBuffer("hello"
); System.out
.println("strBuilder删除索引为1处的字符后结果为："
+ strBuilder.deleteCharAt(1
)); System.out
.println("strBuffer删除索引为1处的字符后结果为："
+ strBuffer.deleteCharAt(1
)); StringBuilder strBuilder2 =new
StringBuilder("hello"
); StringBuffer strBuffer2 =new
StringBuffer("hello"
); System.out
.println("strBuilder2删除索引从1到3（不包括3）的字符后结果为："
+ strBuilder2.delete(1
,3
)); System.out
.println("strBuffer2删除索引从1到3（不包括3）的字符后结果为："
+ strBuffer2.delete(1
,3
)); } }/<code>
执行结果如下图所示：
- 取子字符串
取子字符串的方法如下：
示例代码如下所示：
<code>public
class
StringTest
{public
static
void
main
(String[] args
) { StringBuilder strBuilder =new
StringBuilder("hello world"
); StringBuffer strBuffer =new
StringBuffer("hello world"
); System.out
.println("strBuilder从索引3处开始到字符串末尾的子字符串为："
+ strBuilder.substring(3
)); System.out
.println("strBuffer从索引3处开始到字符串末尾的子字符串为："
+ strBuffer.substring(3
)); StringBuilder strBuilder2 =new
StringBuilder("hello world"
); StringBuffer strBuffer2 =new
StringBuffer("hello world"
); System.out
.println("strBuilder从索引3处开始到5(不包括5)的子字符串为："
+ strBuilder.substring(3
,5
)); System.out
.println("strBuffer从索引3处开始到5(不包括5)的子字符串为："
+ strBuffer.substring(3
,5
)); } }/<code>
执行结果如下图所示：
- 其他
除了以上列举的方法外，还有一些常用的方法，分别为：
- int capacity()：获取容量（初始化字符数组的长度）
- int length()：获取长度(实际字符的长度)
- replace(int start, int end, String str)：将索引从start到end(不包括end)的字符序列替换为str
- char charAt(int index)：获取指定索引出的字符
- void setCharAt(int index, char ch)：用ch替换指定索引处的字符
- void setLength(int newwLength)：将字符序列强制变为指定长度，多余的字符被置为null。
- CharSequence subSequence(int start, int end)：获取子字符序列对象。
- reverse()：将字符序列进行反转。
示例代码如下所示：
<code>public
class
StringTest
{public
static
void
main
(String[] args
) { StringBuilder strBuilder =new
StringBuilder("hello world"
); StringBuffer strBuffer =new
StringBuffer("hello world"
); System.out
.println("strBuilder的容量为："
+ strBuilder.capacity()); System.out
.println("strBuffer的容量为："
+ strBuffer.capacity()); System.out
.println("strBuilder的长度为："
+ strBuilder.length()); System.out
.println("strBuffer的长度为："
+ strBuffer.length()); System.out
.println("用"tom"替换strBuilder的0到5（不包括5）后结果为："
+ strBuilder.replace(0
,5
,"tom"
)); System.out
.println("用"tom"替换strBuffer的0到5（不包括5）后结果为："
+ strBuffer.replace(0
,5
,"tom"
)); System.out
.println("strBuilder的索引为1的字符为："
+ strBuilder.charAt(1
)); System.out
.println("strBuffer的索引为1的字符为："
+ strBuffer.charAt(1
)); strBuilder.setLength(3
); System.out
.println("strBuilder强制变为长度为3的结果为："
+ strBuilder); strBuffer.setLength(3
); System.out
.println("strBuffer强制变为长度为3的结果为："
+ strBuffer); System.out
.println("strBuilder的从0到2的子字符序列为："
+ strBuilder.subSequence(0
,2
)); System.out
.println("strBuffer的从0到2的子字符序列为："
+ strBuffer.subSequence(0
,2
)); System.out
.println("strBuilder的反转后为："
+ strBuilder.reverse()); System.out
.println("strBuffer的反转为："
+ strBuffer.reverse()); } }/<code>
执行结果如下图所示：
自此，关于StringBuffer和StringBuilder的介绍就已经算是结束了。
關鍵字: append strBuffer strBuilder
