Java String class

One, the String class

1. A string is a special object.
2. Once the string is initialized, it cannot be changed.

The String class represents a string and cannot be overridden because it has no subclasses.

Demo:

 1 package com.hpioneer.Demo;
 2 
 3 /**
 4  * @Description: String类
 5  * @Author: HPioneer
 6  * @CreateTime: 2018/5/7  11:13
 7  * @File: Java_String of JavaProject in com.hpioneer.Demo
 8  * @FullFileName: com.hpioneer.Demo.Java_String
 9  * @Create By IntelliJ
10  * @Version: 1.0
11  */
12 public class  Demo_String{
13     public static void main(String[] args) {
14 
15         //字符数组转字符串
16         char[] Array = { 'r', 'u', 'n', 'o', 'o', 'b' };
 17          String string = new String(Array);
 18          System.out.println( string );
 19          System.out.println(string.length()); // Length 
20          System.out.println("1, hello,".concat(string)); // Splicing 
21          System.out.println(2+ " 、hello," + string); // Splice 
22          System.out.printf("The value of the floating-point variable is "+"%f, the value of the integer variable is "+"%d, the value of the string variable is " +"is %s" , 1.0, 1, "1.0"); // Format 
23          System.out.println();
24 
25         String q = "a";
26          String w = "b" ;
 27          String e = q + w;
 28          String r = new StringBuffer().append(q).append(w).toString(); // The implementation of string addition is Buffer After append tostring 
29  
30          String a = "saff" ;
 31          String b = "saff" ;
 32          String c = new String("saff" );
 33          System.out.println(a.equals(b));   // true 
34          System.out.println(a.equals(c));   // true 
35      }
 36  
37}

 

Second, the StringBuffer class

Demo:

 1 package com.hpioneer.Demo;
 2 
 3 /**
 4  * @Description:
 5  * @Author: HPioneer
 6  * @CreateTime: 2018/5/7  11:58
 7  * @File: Demo_StringBuffer of JavaProject in com.hpioneer.Demo
 8  * @FullFileName: com.hpioneer.Demo.Demo_StringBuffer
 9  * @Create By IntelliJ
10  * @Version: 1.0
11  */
12 public class Demo_StringBuffer {
13     public static void main(String[] args) {
14 
15        /* StringBuffer s  = new StringBuffer();
16         System.out.println(s.length());//0
17         System.out.println(s.capacity());//16 初始容量
18 
19         StringBuffer s1  = new StringBuffer(10);
20         System.out.println(s1.length());//0
21         System.out.println(s1.capacity());//10
22 
23         StringBuffer s2  = new StringBuffer("asas");
24         System.out.println(s2.length());//8
25         System.out.println(s2.capacity());//24 = 8+16
26 
27         System.out.println(s2.append(true));//asastrue
28         s2.deleteCharAt(0);
29         s2.delete(0,3);
30         System.out.println(s2.append("dfdfdf"));//truedfdfdf
31         System.out.println(s2.append(100));//truedfdfdf100
32         System.out.println(s2.insert(4,"KK"));//trueKKdfdfdf100
33         System.out.println(s2.reverse());//001fdfdfdKKeurt
34         System.out.println(s2.replace(0,2,"111"));//1111fdfdfdKKeurt
35         System.out.println(s2.substring(2,5));//11f*/
36 
37         /*StringBuffer sb = new StringBuffer("heima");
38 
39         String s1 = new String(sb);                        //通过构造将StringBuffer转换为String
40         System.out.println(s1);
41 
42         String s2 = sb.toString(); //Convert StringBuffer to String by toString method
 43          System.out.println(s2);
 44  
45          String s3 = sb.substring(0, sb.length()); //Pass Convert StringBuffer to String by intercepting substring
 46          System.out.println(s3); */ 
47  
48          String s = "heima" ;
 49          System.out.println(s);
 50          change(s);
 51          System.out .println(s);
 52          // System.out.println(s+="itca"); 
53          System.out.println("-------------------- -" );
 54          StringBuffer sb =new StringBuffer();
55         sb.append("heima");
56         System.out.println(sb);
57         change(sb);
58         System.out.println(sb);
59 
60         
61     }
62 
63    public static void change(StringBuffer sb) {
64         sb.append("itcast");
65     }
66 
67     public static void change(String s) {
68         s += "itcast";
69     }
70     
71 }