写出String类的常用方法以及作用

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1.用字符数组value创建一个String对象
实例:

char[] value ={"a","b","c","d"};
String str = new String(value);
//相当于String str = newString("abcd")

2.用字符数组以x开始的n个字符创建一个String对象
实例:

char[] value ={"a","b","c","d"};
String str = new String(value, 1, 2);
//相当于String str = newString("bc");

3. 获取字符串长度
实例:

String str = new String("478bhjd56");
int strlength = str.length();

4. 获取字符串某一位置的字符
实例:

String str = new String("43dfzyd");
char ch = str.charAt(4);//ch = z

5.获取字符串的子串
实例:

String str1 = newString("asdfzxc");
String str2 = str1.substring(2);//str2 ="dfzxc"
String str3 = str1.substring(2,5);//str3 ="dfz"

6.字符串中字符的大小写转换

public String toLowerCase()
//返回将当前字符串中所有字符转换成小写后的新串

public String toUpperCase()
//返回将当前字符串中所有字符转换成大写后的新串

实例

String str = new String("JavaStudy");
String str1 = str.toLowerCase();
//str1 = "javastudy"
String str2 = str.toUpperCase();
//str2 = "JAVASTUDY"

7.去空格
实例:

String str = " z dali ";
String str1 = str.trim();
int a = str.length();//a = 8
int b = str1.length();//b = 6
System.out.println(a+"\n"+b);

8.基本类型转换为字符串
实例:

String s1 = String.valueOf(12.99);
System.out.println(s1);
//double类型转string类型

9.将字符串分割成字符串数组
实例:

String str = "sgs#jkc#eer";
String[] str1 = str.split("#");
for (int i = 0; i < str1.length; i++) {
  System.out.println(str1[i]);  
  //输出结果是sgs  jkc eer
}