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stringbuffer截取字符串的下标(解析springmvc工作流程)
2022-08-27 13:32:43  浏览:58

stringbuffer截取字符串的下标(解析springmvc工作流程)

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:

public class StringTest { public static void main(String[] args) throws IOException { // 初始化一个容量为16,但没有值的空StringBuffer对象 StringBuffer strBuffer = new StringBuffer(16); System.out.println("strBuffer:" + strBuffer + ", 容量为:" + strBuffer.capacity() + ", 长度为:" + strBuffer.length()); // 初始化一个容量为16,但没有值的空StringBuilder对象 StringBuilder strBuilder = new StringBuilder(16); System.out.println("strBuilder:" + strBuilder + ", 容量为:" + strBuilder.capacity() + ", 长度为:" + strBuilder.length()); // 根据一个字符串初始化一个StringBuffer对象 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()); // 根据一个字符串初始化一个StringBuilder对象 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()); // 根据一个字符序列对象如StringBuilder来初始化一个StringBuffer对象 StringBuilder strBuffer3 = new StringBuilder(strBuilder); System.out.println("strBuffer3的值为:" + strBuffer3 + ", 容量为:" + strBuffer3.capacity() + ", 长度为:" + strBuffer3.length()); // 根据一个字符序列对象如StringBuffer来初始化一个StringBuilder对象 StringBuilder strBuilder3 = new StringBuilder(strBuffer2); System.out.println("strBuilder3的值为:" + strBuilder3 + ", 容量为:" + strBuilder3.capacity() + ", 长度为:" + strBuilder3.length()); }}

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:

public class StringTest { public static void main(String[] args) throws IOException { // 可以拼接所有的基本数据类型 StringBuilder strBuilder = new StringBuilder(); StringBuffer strBuffer = new StringBuffer(); // 拼接int(byte、short都可以自动转换为int) strBuilder.append(12).append(","); strBuffer.append(12).append(","); // 拼接long strBuilder.append(13L).append(","); strBuffer.append(13L).append(","); // 拼接float strBuilder.append(3.4f).append(","); strBuffer.append(3.4f).append(","); // 拼接double strBuilder.append(3.5).append(","); strBuffer.append(3.5).append(","); // 拼接字符数组 strBuilder.append("hello".toCharArray()).append(","); strBuffer.append("hello".toCharArray()).append(","); // 拼接其他引用对象 strBuilder.append(new Date()).append(","); strBuffer.append(new Date()).append(","); // 拼接指定字符数组偏移指定位数后的指定长度字符 strBuilder.append("hello".toCharArray(), 2, 2).append(","); strBuffer.append("hello".toCharArray(), 2, 2).append(","); // 拼接指定字符序列对象(常见的为String、StringBuffer和StringBuilder)指定开始和结束(不包括)的字符串 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)); }}

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:

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"); // indexOf 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)); // lastIndexOf 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)); }}

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:

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)); }}

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:

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)); }}

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:

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)); }}

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:

public class StringTest { public static void main(String[] args) { StringBuilder strBuilder = new StringBuilder("hello world"); StringBuffer strBuffer = new StringBuffer("hello world"); // 获取字符容量 System.out.println("strBuilder的容量为:" + strBuilder.capacity()); System.out.println("strBuffer的容量为:" + strBuffer.capacity()); // 获取长度 System.out.println("strBuilder的长度为:" + strBuilder.length()); System.out.println("strBuffer的长度为:" + strBuffer.length()); // 替换字符串 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")); // 获取指定索引处的字符 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)); // 将字符序列强制变为指定长度 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); // 取子字符序列 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)); // 字符序列反转 System.out.println("strBuilder的反转后为:" + strBuilder.reverse()); System.out.println("strBuffer的反转为:" + strBuffer.reverse()); }}

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。