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String是不变类,用String修改字符串会新建一个String对象,如果频繁的修改,将会产生很多的String对象,开销很大.因此java提供了一个StringBuffer类,这个类在修改字符串方面的效率比String高了很多。
一、关键技术点
1、StringBuffer的indexOf、lastIndexOf、substring、charAt方法的用途和String类一样。
2、append实例方法往字符串尾部添加字符或者字符串。
3、insert实例方法往字符串中间插入字符或字符串。
4、delete和deleteCharAt方法删除字符串中的子串或者字符。
5、replace方法用于替换子串。
6、reverse方法将字符串倒序。
二、实例演示
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/** *//**
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* 文件名:UsingStringBuffer.java
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*/
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package book.oo.String;
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/** *//**
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* 使用StringBuffer类操作字符串
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* @author joe
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*
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*/
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public class UsingStringBuffer ...{
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/** *//**
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* 查找匹配字符串
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*/
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public static void testFindStr() ...{
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StringBuffer sb = new StringBuffer("This is a StringBuffer!");
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//返回子字符串在字符串中最先出现的位置,如果不存在,返回负数
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System.out.println("sb.indexOf(\"is\") = " + sb.indexOf("is"));
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//给indexOf方法设置参数,指定匹配的起始位置
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System.out.println("sb.indexOf(\"is\", 4) = " + sb.indexOf("is", 4));
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//返回子字符串在字符串中最后出现的位置,如果不存在,返回负数
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System.out.println("sb.lastIndexOf(\"is\") = " + sb.lastIndexOf("is"));
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//给lastIndexOf方法设置参数,指定匹配的结束位置
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System.out.println("sb.lastIndexOf("\is\", 1) = " + sb.lastIndexOf("is", 1));
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}
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/** *//**
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* 截取字符串
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*/
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public static void testSubStr() ...{
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StringBuffer sb = new StringBuffer("This is a StringBuffer!");
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//substring方法截取字符串,可以指定截取的起始位置和终止位置
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//默认的终止位置为字符串的末尾
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System.out.println("sb.substring(2) = " + sb.substring(2));
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System.out.println("sb.substring(2, 9) = " + sb.substring(2, 9));
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}
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/** *//**
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* 获取字符串中某个位置上的字符
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*/
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public static void testCharAt() ...{
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StringBuffer sb = new StringBuffer("This is a StringBuffer!");
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//返回字符串中某个位置上的字符
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System.out.println("sb.charAt(2) = " + sb.charAt(2));
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}
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/** *//**
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* 添加各种类型的数据到字符串尾部
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*/
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public static void testAppend() ...{
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StringBuffer sb = new StringBuffer("This is a StringBuffer!");
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//添加字符或者字符数组到StringBuffer的末尾
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sb.append('I');
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sb.append(new char[]...{' ', 'a', 'm'});
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System.out.println("Append char:" + sb.toString());
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//添加字符串到StringBuffer的末尾
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sb.append(" in 、Beijing.");
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System.out.println("Append String: " + sb.toString());
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//添加基本数字
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sb.append(15);
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sb.append(1.23f);
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sb.append(3.4d);
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sb.append(899L);
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System.out.println("Append number: " + sb.toString());
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//添加布尔值
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sb.append(false);
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sb.append(true);
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System.out.println("Append boolean: " + sb.toString());
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}
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/** *//**
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* 删除字符串中的数据
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*/
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public static void testDelete() ...{
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StringBuffer sb = new StringBuffer("This is a StringBuffer!");
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//删除指定位置的字符
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sb.deleteCharAt(1);
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sb.deleteCharAt(2);
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System.out.println("Delete char: " + sb.toString());
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//删除指定范围的字符串
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sb.delete(1, 5);
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System.out.println("sb.delete(1, 5) = " + sb.toString());
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}
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/** *//**
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* 向字符串中插入各种类型的数据
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*/
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public static void testInsert() ...{
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StringBuffer sb = new StringBuffer("This is a StringBuffer!");
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//能够在指定位置插入字符、字符数组、字符串以及各种数字和布尔值
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sb.insert(2, 'W');
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sb.insert(3, new char[]...{'A', 'B', 'C'});
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sb.insert(8, "abc");
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sb.insert(2, 3);
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sb.insert(3, 2.3f);
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sb.insert(6, 3.75d);
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sb.insert(5, 9843L);
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sb.insert(2, true);
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System.out.println("testInsert: " + sb.toString());
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}
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/** *//**
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* 替换字符串中的某些字符
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*/
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public static void testReplace() ...{
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StringBuffer sb = new StringBuffer("This is a StringBuffer!");
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//将字符串中某段字符替换成另一个字符串
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sb.replace(3, 8, "replace");
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System.out.println("testReplace: " + sb.toString());
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}
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/** *//**
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* 将字符串倒序
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*/
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public static void reverseStr() ...{
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StringBuffer sb = new StringBuffer("This is a StringBuffer!");
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System.out.println(sb.reverse()); //reverse方法将字符串倒序
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}
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public static void main(String[] args) ...{
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StringBuffer sb = new StringBuffer("This is a StringBuffer!");
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System.out.println("原始StringBuffer: " + sb.toString());
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UsingStringBuffer.testFindStr();
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UsingStringBuffer.testSubStr();
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UsingStringBuffer.testCharAt();
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UsingStringBuffer.testAppend();
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UsingStringBuffer.testDelete();
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UsingStringBuffer.testInsert();
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UsingStringBuffer.testReplace();
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UsingStringBuffer.reverseStr();
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}
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}
输出结果:
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原始StringBuffer: This is a StringBuffer!
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sb.indexOf("is") = 2
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sb.indexOf("is", 4) = 5
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sb.lastIndexOf("is") = 5
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sb.lastIndexOf("is", 1) = -1
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sb.substring(2) = is is a StringBuffer!
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sb.substring(2, 9) = is is a
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sb.charAt(2) = i
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Append char:This is a StringBuffer!I am
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Append String: This is a StringBuffer!I am in 、Beijing.
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Append number: This is a StringBuffer!I am in 、Beijing.151.233.4899
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Append boolean: This is a StringBuffer!I am in 、Beijing.151.233.4899falsetrue
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Delete char: Ti is a StringBuffer!
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sb.delete(1, 5) = T a StringBuffer!
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testInsert: Thtrue32.984333.75WABCisabc is a StringBuffer!
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testReplace: Thireplacea StringBuffer!
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小结:
StringBuffer不是不变类,在修改字符串内容时,不会创建新的对象,因此,它比String类更适合修改字符串。
StringBuffer类没有提供同String一样的toCharArray方法
StringBuffer类的replace方法同String类的replace方法不同,它的replace方法有三个参数,第一个参数指定被替换子串的起始位置,第二个参数指定被替换子串的终止位置,第三个参数指定新子串
本文来自ChinaUnix博客,如果查看原文请点:http://blog.chinaunix.net/u/12056/showart_454574.html |
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