JAVA笔记07 STRING类

JAVA笔记06 STRING类

一，字节数组转换成为字符数组（构造方法）

public class Demo5 {
    public static void main(String[] args) {
byte[] bytes = {98,99,100,101};// 字节数组转换成为字符数组（构造方法）
String  string =  new String(bytes,0,3);
 System.out.println(string);

二，字符串转换成字节数组（使用getBytes）

public class Demo5 {
    public static void main(String[] args) {
    String string = "abcde"; //字符串转换成字节数组（使用getBytes）
        byte[] bytes=string.getBytes();
         for (int i = 0; i < bytes.length; i++) {
         System.out.println(bytes[i]);
         };

三.字符数组转换成字符串

public class Demo5 {
    public static void main(String[] args) {
char[] ch = {'a','b','c','d'};  //字符数组转换成字符串    String str = new String(ch,2,2);
System.out.println(str);
String str = String.valueOf(ch);
System.out.println(str);

四.字符串转换成字符数组

 public class Demo5 {
    public static void main(String[] args) {
 String str = "abcde";   //字符串转换成字符数组
 char[] ch = str.toCharArray();
 for (int i = 0; i < ch.length; i++) {
 System.out.println(ch[i]);
 }

五，转换大小写

public class Demo5 {
    public static void main(String[] args) {
String s = "abcd".toUpperCase();   //大写
 System.out.println(s);    

String s ="ABCD".toLowerCase();
System.out.println(s);  //小写

六.链式编程

public class Demo5 {
    public static void main(String[] args) {
String s = "abc".concat("sss").concat("hhh");  //  lian shi bian  cheng
System.out.println(s);

七，练习

public class Demo5 {
    public static void main(String[] args) {
String a = "dYiDhRaf";  
 String a1= a.substring(0,1).toUpperCase().concat(a.substring(1).toLowerCase());
 System.out.println(a1);

八.新旧替换

public class Demo5 {
    public static void main(String[] args) {
String s= "朱波波爱撩妹".replace("撩","*").replace("妹","*");
 System.out.println(s);

九.去掉前后空格

public class Demo5 {
    public static void main(String[] args) {
String  s = "   ssdff   ";
System.out.println(s);
String s1 = "    asdf    ".trim();
 System.out.println(s1);

十.去掉前或后空格

 public class Demo5 {
    public static void main(String[] args) {
 String str2 = "";
    for (int i = 0; i < a.length(); i++) {
       char ch = a.charAt(i);
        if(ch == ' ' ){
            continue;
        }else{
            str2+=ch;
        }
    }
    System.out.println(str2);
}

十 一. 练习题（把数组按要求转换成字符串）

 public class Demo5 {
    public static void main(String[] args) {
int[] a = {1,2,3};   //把数组变成字符串
String str = "[";
for (int i = 0; i < a.length; i++) {
    if(i == a.length-1){
        str = str+a[i]+"]";
    }else{
        str= str + a[i]+",";
    }
}
System.out.println(str);

十二. 字符串反转

public class Demo5 {
    public static void main(String[] args) {
Scanner scanner  =  new Scanner(System.in);  //字符串反转
System.out.println("请输入");
String str = scanner.nextLine();
String str1 = "";
for (int i = str.length()-1; i >=0; i--) {
   str1 += str.charAt(i);
 }
 System.out.println(str1);

十三. 检索

public class Demo5 {
    public static void main(String[] args) {
String str = "woaijavawojiuaijavaworenaijavawozuiaijava";
int count = 0;
int index = str.indexOf("java");
System.out.println(index);
while (index!=-1){
    count++;
    str = str.substring(index+4);
    index = str.indexOf("java");
}
 System.out.println(count);
    }
}