Java中表示字符串的有三個類：String、StringBuffer和StringBuilder。其中，String的長度是不可變的，而StringBuffer和StringBuilder是長度可變的。對於StringBuffer和StringBuilder來說，兩者的API幾乎一模一樣，因為兩者有共同的父類：AbstractStringBuilder。區別在於StringBuffer的大部分方法都是被synchronized關鍵字修飾，是線程安全的，而StringBuilder則與其相反。
所以本篇就對StringBuffer和StringBuilder類比著來進行介紹。
- 構造器
StringBuffer和StringBuilder的構造器都有三個，分別如下：
StringBuffer的構造器：
- new StringBuffer(int capacity)
- new StringBuffer(String str)
- new StringBuffer(CharSequence seq)
StringBuilder的構造器：
- new StringBuilder(int capacity)
- new StringBuilder(String str)
- new StringBuilder(CharSequence seq)
對比兩者構造器發現，它們對構造器的重載都施行了同樣的方式，可以傳入一個整數的容量，可以傳一個字符串值，甚至可以傳一個字符序列的對象。對於Java來說，常用的字符序列對象就是我們認知中的String， StringBuffer和StringBuilder。關於StringBuilder和StringBuffer的使用的示例代碼如下所示：
<code>public
class
StringTest
{public
static
void
main
(String[] args
) throws IOException { StringBuffer strBuffer =new
StringBuffer(16
); System.out
.println("strBuffer："
+ strBuffer +", 容量為："
+ strBuffer.capacity() +", 長度為："
+ strBuffer.length()); StringBuilder strBuilder =new
StringBuilder(16
); System.out
.println("strBuilder："
+ strBuilder +", 容量為："
+ strBuilder.capacity() +", 長度為："
+ strBuilder.length()); StringBuffer strBuffer2 =new
StringBuffer("how are you"
); System.out
.println("strBuffer2的值為："
+ strBuffer2 +", 容量為："
+ strBuffer2.capacity() +", 長度為："
+ strBuffer2.length()); StringBuilder strBuilder2 =new
StringBuilder("how old are you"
); System.out
.println("strBuilder2的值為："
+ strBuilder2 +", 容量為："
+ strBuilder2.capacity() +", 長度為："
+ strBuilder2.length()); StringBuilder strBuffer3 =new
StringBuilder(strBuilder); System.out
.println("strBuffer3的值為："
+ strBuffer3 +", 容量為："
+ strBuffer3.capacity() +", 長度為："
+ strBuffer3.length()); StringBuilder strBuilder3 =new
StringBuilder(strBuffer2); System.out
.println("strBuilder3的值為："
+ strBuilder3 +", 容量為："
+ strBuilder3.capacity() +", 長度為："
+ strBuilder3.length()); } }/<code>
執行結果如下圖所示：
- 拼接參數
拼接參數常用的方法方法如下圖：
也就是說，該方法可以拼接所有的基本數據類型和其對應的包裝類型，字符數組、字符序列對象及其他的引用對象等。
StringBuilder和StringBuffer的append
其示例代碼如下所示：
<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信息為：\n"
+ Arrays.asList(strArr));
}
private static void printStrBuffer(StringBuffer strBuffer) {
String[] strArr = strBuffer.deleteCharAt(strBuffer.length() - 1
).toString().split(","
);
System.out.println
("StringBuffer信息為：\n"
+ Arrays.asList(strArr));
}
}
/<code>只想結果如下圖所示：
- 獲取某個字符串在另一個字符串中的索引位置
這裡使用的方法有四個，如下圖：
相關的示例代碼如下所示：
<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中首次出現的位置為："
+ strBuilder.indexOf("no"
)); System.out
.println(""no"在strBuffer中首次出現的位置為："
+ strBuffer.indexOf("no"
)); System.out
.println(""no"在strBuilder中在索引3之後首次出現的位置為："
+ strBuilder.indexOf("no"
,3
)); System.out
.println(""no"在strBuffer中在索引3之後首次出現的位置為："
+ strBuffer.indexOf("no"
,3
)); System.out
.println(""no"在strBuilder中最後出現的位置為："
+ strBuilder.lastIndexOf("no"
)); System.out
.println(""no"在strBuffer中最後出現的位置為："
+ strBuffer.lastIndexOf("no"
)); System.out
.println(""no"在strBuilder中在索引20之前最後出現的位置為："
+ strBuilder.lastIndexOf("no"
,20
)); System.out
.println(""no"在strBuffer中在索引20之前最後出現的位置為："
+ strBuffer.lastIndexOf("no"
,20
)); } } /<code>
執行結果如下圖所示：
- 插入方法
插入方法為：insert(int offset, XXX xxx）, 目的是在偏移offset個字符後插入xxx。這裡的xxx表示所有的基本數據類型及其對應的包裝類型、字符數組、字符序列對象和其他的引用對象等。常用方法如下：
相關示例代碼如下所示：
<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位後插入整數3的結果為："
+ strBuilder.insert(2
,3
)); System.out
.println("在strBuffer偏移3位後插入整數3的結果為："
+ strBuffer.insert(3
,3
)); StringBuilder strBuilder2 =new
StringBuilder("world"
); StringBuffer strBuffer2 =new
StringBuffer("world"
); System.out
.println("在strBuilder2偏移2位後插入'好'的結果為："
+ strBuilder2.insert(2
,'好'
)); System.out
.println("在strBuffer2偏移3位後插入'好'的結果為："
+ strBuffer2.insert(3
,'好'
)); StringBuilder strBuilder3 =new
StringBuilder("what"
); StringBuffer strBuffer3 =new
StringBuffer("what"
); System.out
.println("在strBuilder3偏移2位後插入4L的結果為："
+ strBuilder3.insert(2
,4L
)); System.out
.println("在strBuffer3偏移3位後插入4L的結果為："
+ strBuffer3.insert(3
,4L
)); StringBuilder strBuilder4 =new
StringBuilder("where"
); StringBuffer strBuffer4 =new
StringBuffer("where"
); System.out
.println("在strBuilder4偏移2位後插入3.14F的結果為："
+ strBuilder4.insert(2
,3.14F
)); System.out
.println("在strBuffer4偏移3位後插入3.14F的結果為："
+ strBuffer4.insert(3
,3.14F
)); StringBuilder strBuilder5 =new
StringBuilder("when"
); StringBuffer strBuffer5 =new
StringBuffer("when"
); System.out
.println("在strBuilder5偏移2位後插入1.414的結果為："
+ strBuilder5.insert(2
,1.414
)); System.out
.println("在strBuffer5偏移3位後插入1.414的結果為："
+ strBuffer5.insert(3
,1.414
)); StringBuilder strBuilder6 =new
StringBuilder("crazy"
); StringBuffer strBuffer6 =new
StringBuffer("crazy"
); System.out
.println("在strBuilder6偏移2位後插入true的結果為："
+ strBuilder6.insert(2
,true
)); System.out
.println("在strBuffer6偏移3位後插入false的結果為："
+ strBuffer6.insert(3
,false
)); StringBuilder strBuilder7 =new
StringBuilder("hehe"
); StringBuffer strBuffer7 =new
StringBuffer("hehe"
); System.out
.println("在strBuilder7偏移2位後插入Date的結果為："
+ strBuilder7.insert(2
,new
Date())); System.out
.println("在strBuffer7偏移3位後插入Date的結果為："
+ strBuffer7.insert(3
,new
Date())); StringBuilder strBuilder8 =new
StringBuilder("this"
); StringBuffer strBuffer8 =new
StringBuffer("this"
); System.out
.println("在strBuilder8偏移2位後插入字符數組['a', 'r', 'e']的結果為："
+ strBuilder8.insert(2
,new
char
[]{'a'
,'r'
,'e'
})); System.out
.println("在strBuffer8偏移3位後插入字符數組['a', 'r', 'e']的結果為："
+ 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位後插入Date的結果為："
+ strBuilder9.insert(2
,new
StringBuffer("234"
))); System.out
.println("在strBuffer9偏移3位後插入Date的結果為："
+ strBuffer9.insert(3
,new
StringBuilder("234"
))); StringBuilder strBuilder10 =new
StringBuilder("that"
); StringBuffer strBuffer10 =new
StringBuffer("that"
); System.out
.println("在strBuilder10偏移2位後插入字符數組['a', 'r', 'e']的結果為："
+ strBuilder10.insert(2
,new
char
[]{'a'
,'r'
,'e'
},0
,2
)); System.out
.println("在strBuffer10偏移3位後插入字符數組['a', 'r', 'e']的結果為："
+ 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位後插入Date的結果為："
+ strBuilder11.insert(2
,new
StringBuffer("234"
),0
,2
)); System.out
.println("在strBuffer11偏移3位後插入Date的結果為："
+ strBuffer11.insert(3
,new
StringBuilder("234"
),0
,2
)); } }/<code>
執行結果如下圖所示：
- 刪除某個或某些字符
刪除某個或某些的字符方法如下圖所示：
相關示例代碼如下：
<code>public
class
StringTest
{public
static
void
main
(String[] args
) { StringBuilder strBuilder =new
StringBuilder("hello"
); StringBuffer strBuffer =new
StringBuffer("hello"
); System.out
.println("strBuilder刪除索引為1處的字符後結果為："
+ strBuilder.deleteCharAt(1
)); System.out
.println("strBuffer刪除索引為1處的字符後結果為："
+ strBuffer.deleteCharAt(1
)); StringBuilder strBuilder2 =new
StringBuilder("hello"
); StringBuffer strBuffer2 =new
StringBuffer("hello"
); System.out
.println("strBuilder2刪除索引從1到3（不包括3）的字符後結果為："
+ strBuilder2.delete(1
,3
)); System.out
.println("strBuffer2刪除索引從1到3（不包括3）的字符後結果為："
+ strBuffer2.delete(1
,3
)); } }/<code>
執行結果如下圖所示：
- 取子字符串
取子字符串的方法如下：
示例代碼如下所示：
<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從索引3處開始到字符串末尾的子字符串為："
+ strBuilder.substring(3
)); System.out
.println("strBuffer從索引3處開始到字符串末尾的子字符串為："
+ strBuffer.substring(3
)); StringBuilder strBuilder2 =new
StringBuilder("hello world"
); StringBuffer strBuffer2 =new
StringBuffer("hello world"
); System.out
.println("strBuilder從索引3處開始到5(不包括5)的子字符串為："
+ strBuilder.substring(3
,5
)); System.out
.println("strBuffer從索引3處開始到5(不包括5)的子字符串為："
+ strBuffer.substring(3
,5
)); } }/<code>
執行結果如下圖所示：
- 其他
除了以上列舉的方法外，還有一些常用的方法，分別為：
- int capacity()：獲取容量（初始化字符數組的長度）
- int length()：獲取長度(實際字符的長度)
- replace(int start, int end, String str)：將索引從start到end(不包括end)的字符序列替換為str
- char charAt(int index)：獲取指定索引出的字符
- void setCharAt(int index, char ch)：用ch替換指定索引處的字符
- void setLength(int newwLength)：將字符序列強制變為指定長度，多餘的字符被置為null。
- CharSequence subSequence(int start, int end)：獲取子字符序列對象。
- reverse()：將字符序列進行反轉。
示例代碼如下所示：
<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的容量為："
+ strBuilder.capacity()); System.out
.println("strBuffer的容量為："
+ strBuffer.capacity()); System.out
.println("strBuilder的長度為："
+ strBuilder.length()); System.out
.println("strBuffer的長度為："
+ strBuffer.length()); System.out
.println("用"tom"替換strBuilder的0到5（不包括5）後結果為："
+ strBuilder.replace(0
,5
,"tom"
)); System.out
.println("用"tom"替換strBuffer的0到5（不包括5）後結果為："
+ strBuffer.replace(0
,5
,"tom"
)); System.out
.println("strBuilder的索引為1的字符為："
+ strBuilder.charAt(1
)); System.out
.println("strBuffer的索引為1的字符為："
+ strBuffer.charAt(1
)); strBuilder.setLength(3
); System.out
.println("strBuilder強制變為長度為3的結果為："
+ strBuilder); strBuffer.setLength(3
); System.out
.println("strBuffer強制變為長度為3的結果為："
+ strBuffer); System.out
.println("strBuilder的從0到2的子字符序列為："
+ strBuilder.subSequence(0
,2
)); System.out
.println("strBuffer的從0到2的子字符序列為："
+ strBuffer.subSequence(0
,2
)); System.out
.println("strBuilder的反轉後為："
+ strBuilder.reverse()); System.out
.println("strBuffer的反轉為："
+ strBuffer.reverse()); } }/<code>
執行結果如下圖所示：
自此，關於StringBuffer和StringBuilder的介紹就已經算是結束了。
關鍵字: append strBuffer strBuilder
