Use java development experience -String class
String s = null; // null space that is not allocated heap memory
String a; // allocate a memory space, without any object stored
String a = ""; // allocate a memory space, a String object saved
Common method
public class StringTest {
public static void main(String[] args) {
String str1 = new String();
System.out.println(str1);
String str2 = new String("asdf");
System.out.println(str2);
char[] value = {'a','b','c','d'};
String str3 = new String(value);
System.out.println(str3);
String str4 = new String(value, 1, 2);
System.out.println(str4);
byte[] strb = new byte[]{65,66};
String str5 = new String(strb);
System.out.println(str5);
String str = new String("asdfzxc");
int strlength = str.length();
System.out.println(strlength);
char ch = str.charAt(4);//ch = z
System.out.println(ch);
//该方法从beginIndex位置起,从当前字符串中取出剩余的字符作为一个新的字符串返回
String str6 = str.substring(2);//str2 = "dfzxc"
System.out.println(str6);
//该方法从beginIndex位置起,从当前字符串中取出到endIndex-1位置的字符作为一个新的字符串返回。
String str7 = str.substring(2,5);//str3 = "dfz"
System.out.println(str7);
String str8 = new String("abc");
String str9 = new String("ABC");
int a = str8.compareTo(str9);//a>0
int b = str8.compareToIgnoreCase(str9);//b=0
boolean c = str8.equals(str9);//c=false
boolean d = str8.equalsIgnoreCase(str9);//d=true
//相当于String str = "aa"+"bb"+"cc";
String str10 = "aa".concat("bb").concat("cc");
System.out.println(str10);
String str11 = "I am a good student";
//于查找当前字符串中字符或子串,返回字符或子串在当前字符串中从左边起首次出现的位置,若没有出现则返回-1。
int aa = str11.indexOf('a');//a = 2
int bb = str11.indexOf("good");//b = 7
//从fromIndex位置向后查找。
int cc = str11.indexOf("w",2);//c = -1
//区别在于该方法从字符串的末尾位置向前查找。
int dd = str11.lastIndexOf("a");//d = 5
int ee = str11.lastIndexOf("a",3);//e = 2
String str00 = new String("asDF");
String str111 = str00.toLowerCase();//str1 = "asdf"
System.out.println(str111);
String str222 = str00.toUpperCase();//str2 = "ASDF"
System.out.println(str222);
String str0 = "asdzxcasd";
String str100 = str0.replace('a','g');//str1 = "gsdzxcgsd"
String str200 = str0.replace("asd","fgh");//str2 = "fghzxcfgh"
String str300 = str0.replaceFirst("asd","fgh");//str3 = "fghzxcasd"
String str400 = str0.replaceAll("asd","fgh");//str4 = "fghzxcfgh"
String str33 = " a sd ";
String str13 = str33.trim();
System.out.println(str13);
String strR = "asdfgh";
boolean aA = strR.startsWith("as");//a = true
System.out.println(aA);
boolean bB = strR.endsWith("gh");//b = true
System.out.println(bB);
String strC = "student";
System.out.println(strC.contains("stu"));//true
System.out.println(strC.contains("ok"));//false
String strS = "asd!qwe|zxc#";
String[] strss = str.split("!|#");
//str1[0] = "asd";str1[1] = "qwe";str1[2] = "zxc";
System.out.println(strss.toString());
//字符串转换为基本类型
int n = Integer.parseInt("12");
System.out.println(n);
float f = Float.parseFloat("12.34");
System.out.println(f);
double D = Double.parseDouble("1.124");
System.out.println(D);
//基本类型转换为字符串类型
String s111 = String.valueOf(12);
System.out.println(s111);
String s122 = String.valueOf(12.34);
System.out.println(s122);
//进制转换
String binaryString = Long.toBinaryString(7);
System.out.println(binaryString);
}
}