Traversal and splicing of strings

Traversal of string ：

demand : Enter a string on the keyboard , Use the program to traverse the string in the console

 Ideas :
① Enter a string on the keyboard , use Scanner Realization 
② Traversal string , First, you need to be able to get every character in the string 
    ●public char charAt(int index): Returns the char value , The index of the string is also from 0 At the beginning 
③ Traversal string , Secondly, we should be able to get the length of the string 
    ●public int length(): Returns the length of this string 
    ● Length of array : Array name .length
    ● Length of string :  String object .length()
④ The general format for traversing strings 

 for(int i=0; i<s.length(); i++) {
    
        s. charAt(i); //  Is the character value at the specified index 
    }

import java.util.Scanner;

public class _02_String {
    
    public static void main(String[] args) {
    
        // Enter a string on the keyboard , use Scanner Realization 
        Scanner sc = new Scanner(System.in);
        System.out.println(" Please enter a string ：");
        String line = sc.nextLine();

        // Traversal string , First, you need to be able to get every character in the string 
        for (int i = 0; i < line.length(); i++) {
    
            System.out.println(line.charAt(i));
        }
    }
}

String splicing

demand : Define a method , hold int The data in the array is spliced into a string according to the specified format , Call the method , And output the results on the console . for example , The array is int[] arr= {1,2,3};, After executing the method, the output is : [1,2, 3]

 Ideas :
① Define a int An array of types , Complete the initialization of array elements with static initialization 
② Define a method , Used for holding int The data in the array is spliced into a string according to the specified format . return type String, parameter list int[] arr
③ Traversing arrays in methods , Splice as required 
④ Calling method , Receive the result with a variable 
⑤ Output results 

public class _04_String {
    
    public static void main(String[] args) {
    
        // Define a int An array of types , Complete the initialization of array elements with static initialization 
        int[] arr = {
    1, 2, 3};

        // Calling method , Receive the result with a variable 
        String s = arrayToString(arr);

        // Output results 

        System.out.println("s:" + s);
    }

    // Define a method , Used for holding int The data in the array is spliced into a string according to the specified format 
    /*  Two clear :  return type : String  Parameters : int[] arr */
    public static String arrayToString(int[] arr) {
    
        String s = "";
        // Traversing arrays in methods , Splice as required 
        s = s + "[";
        for (int i = 0; i < arr.length; i++) {
    
            if (i == arr.length - 1) {
    
                s = s + arr[i];
            } else {
    
                s = s + arr[i] + ',';
            }
        }
        s = s + "]";
        return s;
    }
}