String類(lèi)：

????str = str1.concat("DEF123");//拼接字符串，并返回新的字符串

????str = str1.substring(2);//從開(kāi)始下標(biāo)處截取到字符串末尾，并返回新的字符串

????str = str1.substring(2,5);//從開(kāi)始下標(biāo)處截取到結(jié)束下標(biāo)處（左閉右開(kāi)），并返回新的字符串

????str = str1.toUpperCase();//轉(zhuǎn)大寫(xiě)

????str = str1.toLowerCase();//轉(zhuǎn)小寫(xiě)

????str = str1.trim();//去首尾空格

????str = str1.replace("s","a");//替換

????str = str1.replaceAll("sss","a");

????System.out.println("判斷兩個(gè)字符串內(nèi)容是否相同（區(qū)分大小寫(xiě)）："+str1.equals("123321"));

????System.out.println("判斷兩個(gè)字符串內(nèi)容是否相同（不區(qū)分大小寫(xiě)）："+str1.equalsIgnoreCase("123321"));

????System.out.println("判斷字符串是否是以某個(gè)字符串開(kāi)頭："+str1.startsWith("123321"));

????System.out.println("判斷字符串是否是以某個(gè)字符串結(jié)尾："+str1.endsWith("123321"));

????System.out.println(" 判斷字符串第一次出現(xiàn)的下標(biāo)："+str1.indexOf("1"));

????System.out.println(" 判斷字符串最后一次出現(xiàn)的下標(biāo)："+str1.lastIndexOf("1"));

????System.out.println(" 獲取指定下標(biāo)的字符："+str1.charAt(11));

????char[] chars = str1.toCharArray();//將在字符串轉(zhuǎn)成字符數(shù)組

????System.out.println(Arrays.toString(chars));

????System.out.println(String.valueOf(100));//將其他類(lèi)型轉(zhuǎn)字符串

StringBuffer:

????sb.append("123abc");//在末尾追加字符串

????sb.append("456def");

????sb.insert(5,"321");//在在指定位置插入字符串

????sb.replace(6,12,"xxyy");//從開(kāi)始下標(biāo)替換到結(jié)束下標(biāo)

????sb.deleteCharAt(5);//刪除指定下標(biāo)的字符

????sb.delete(0,2);//刪除從開(kāi)始到結(jié)束下標(biāo)的字符

????sb.reverse();//反轉(zhuǎn)字符

深入String：??

?????//深入String :創(chuàng)建對(duì)象問(wèn)題

????//面試題一：一下代碼會(huì)創(chuàng)建幾個(gè)string對(duì)象？

????//答案：一個(gè),"abc"存在常量池里，常量池中的數(shù)據(jù)是唯一的

????String str1 = "abc";

????String str2 = "abc";

????System.out.println(str1==str2);

????//面試題一：一下代碼會(huì)創(chuàng)建幾個(gè)string對(duì)象？

????//答案：3個(gè),"abc"存在常量池里，new 了2個(gè)

????String str1 = new String("abc");

????String str2 = new String("abc");

?????深入String :拼接字符串問(wèn)題

????String str1 = "abc";

????String str2 = "abc";

????System.out.println(str1==str2);

????//注意：字面值常量在編譯時(shí)就直接拼接

????String str3 = "ab" + "c";

????System.out.println(str1==str3);//true

????final String s1 = "ab";

????final String s2 = "c";

????String str4 = s1+s2;

????System.out.println(str4==str1);//true

????String s3 = "ab";

????String s4 = "c";

????String s5 = s3+s4;//底層實(shí)現(xiàn)： new StringBuidler(Sting.valueOf(s3)).append(s4).toString()

????System.out.println(str1==s5);//false