String字符串常见的基本操作

String字符串常见的基本操作

（1）新建字符串

String str = new String("abc");
String str2 = new String(new char[]{'a','b','c'});
String str3 = "abc";
String str4 = new String(new char[]{'1','a','b','c'},1,3); //从索引1开始  往后搞3个元素
System.out.println(str);//abc
System.out.println(str2);//abc
System.out.println(str3);//abc
System.out.println(str4);//abc

（2)获取字符串的内容信息

String str5 = "hello everyone, my name is yangxu ,i am chinese";
System.out.println("字符串的长度是："+str5.length());//47
System.out.println("首次出现a的索引是："+str5.indexOf('a'));//20
System.out.println("最后一次出现a的索引是："+str5.lastIndexOf('a'));//37
System.out.println("索引为2的字符是："+str5.charAt(2));//l

(3)获取子字符串

String str6 = str5.substring(20); //返回从索引2开始子字符串
System.out.println(str6); //ame is yangxu ,i am chinese
String str7 = str5.substring(2,5); //返回索引2到索引5的子字符串，包括2不包括5
System.out.println(str7); //llo

(4)去除空格

String str8 = "    java    python   ";
System.out.println("去掉空格后的子字符串："+str8.trim());//java    python
System.out.println("去掉空格后的子字符串的长度是："+str8.trim().length()); //14  只去掉首尾空格

(5)字符串替换

String str9 = "address";
System.out.println(str9.replace("a","A"));//Address
System.out.println(str9);//address

(6)判断字符串的开始于结尾

String str10 = "yangxunihao";
System.out.println(str10.startsWith("yang"));//true
System.out.println(str10.endsWith("java")); //false

(7)判断字符串是否相等

String strs1=new String("abc");
String strs2 = new String("ABC");
String strs3 = "abc";
String strs4 = new String(new char[]{'a','b','c'});
String strs5 = "ab"+"c";

System.out.println(strs1 == strs2); //false
System.out.println(strs1.equals(strs2));//false
System.out.println(strs1.equalsIgnoreCase(str2)); //true

System.out.println(strs1==strs3); //false
System.out.println(strs1.equals(strs3)); //true

System.out.println(strs1==strs4); //false
System.out.println(strs1.equals(strs4)); //true


System.out.println(strs3==strs4); //false
System.out.println(strs3.equals(strs4));//true

System.out.println(strs3==strs5); //true
System.out.println(strs3.equals(strs5)); //true

(8)字母大小写转换

System.out.println(strs1.toUpperCase());//ABC
System.out.println(strs1.toLowerCase());//abc

(9)字符串分割

String strs6 = "192.168.0.1";
String []arr = strs6.split("\\.");
System.out.println(Arrays.toString(arr));//[192, 168, 0, 1]

(10)包含子串问题

String sqls = "yangxu";
System.out.println(sqls.indexOf("xu"));//4  xu第一次出现的索引是4

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