将每个字符的字符串打印两次 package com.pack7； /*任务是获取一个字符串并再次打印该字符串，但这次每次 *字符打印两次。假设输入为：“java”，输出为：“jjaavvaa” */ 公共B类{ 公共字符串doubleChar（字符串str） { char[]ch=str.toCharArray（）；//将给定字符串转换为char数组 char[]ch2=new char[ch.length*2]；//创建了另一个长度为第一个数组两倍的数组 对于（inti=0；i

这是一个愚蠢的程序。你的循环覆盖了上一次迭代 字符，因为您没有正确计算ch2索引。请尝试以下操作：

package com.pack7;
/* The task is to take a string and print the string again but this time every 
 *character print twice. say input is:"java", output should be :"jjaavvaa" 
 */
public class ClassB {
    
    public String doubleChar(String str)
    {
        char[] ch = str.toCharArray();//converted the given string to char array
        char[] ch2 = new char[ch.length*2];//created another array of twice the length of first array
        for(int i=0;i<ch.length;i++)
        {
            ch2[i]=ch[i];//assigning 1st char of 1st array in the 2nd array(index 0)
            ch2[i+1]=ch[i];//assigning 1st char of 1st array in the 2nd array(index 0+1)
        }
        
        String result = new String(ch2);//and passing the 2nd array as parameter to create string
        return result;// returning the string as answer
        
    }
    
    public static void main(String[] args) 
    {
        ClassB obj = new ClassB();
        String s = obj.doubleChar("java");
        System.out.println(s);//but it prints "javaa", i can't figure out why my logic is not working
    }

}

---

for（int i=0；i您正在用下一个字符（下一个i位置）覆盖您添加的第二个字符。
for(int i=0;i<ch.length;i++)
{
    ch2[2*i]=ch[i];//assigning 1st char of 1st array in the 2nd array(index 0)
    ch2[2*i+1]=ch[i];//assigning 1st char of 1st array in the 2nd array(index 0+1)
}