java 使用子字符串向后显示字符串
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Displaying a string backwards using substring
提问by First Lady
I have here a method that displays a string backward.
我在这里有一个向后显示字符串的方法。
public static String ReverseStr(String backward) {
String newString = "";
for (int i=0; i<backward.length(); i++) {
newString = backward.charAt(i) + newString;
}
return newString;
}
It works properly but I'd like to do it in another way, that is, using a for loop, getting each character in the string using substring method with two parameters, starting with the last character then concatenates that one-character substring with the new string each time through the loop.
I tried this:
它工作正常，但我想以另一种方式进行，即使用for 循环，使用substring 带有两个参数的方法获取字符串中的每个字符，从最后一个字符开始，然后将该单字符子字符串与新字符串连接起来每次通过循环。
我试过这个：
public static String ReverseStr(String backward) {
String newString = "";
for (int i=0; i>backward.length(); i--) {
String subChar = backward.substring(backward.length()-1);
newString += subChar;
}
return newString;
}
But when I run the program, it displays nothing. Please help me fix the code. Thank you very much!
但是当我运行程序时，它什么也没显示。请帮我修复代码。非常感谢你！
回答by
If this is not a homework, then use StringBuilder class and reverse() method.
如果这不是作业，那么使用 StringBuilder 类和 reverse() 方法。
http://docs.oracle.com/javase/1.5.0/docs/api/java/lang/StringBuilder.html#reverse()
http://docs.oracle.com/javase/1.5.0/docs/api/java/lang/StringBuilder.html#reverse()
If this is a homework do it by yourself.
如果这是家庭作业，请自己做。
回答by Tomasz Nurkiewicz
The loop never executes due to wrong control condition:
由于错误的控制条件，循环永远不会执行：
for (int i=0; i>backward.length(); i--)
It starts from 0and continues until iis greater than length(which is never true as lengthis always at least 0). You probablymeant:
它从开始0并一直持续到i大于length（这永远不会正确length，至少总是如此0）。你可能的意思是：
for (int i=backward.length(); i>=0; i--)
Once you manage to fix your code, consider using StringBuilderinstead of concatenating to String. And once you manage to use StringBuilder, you'll discover handy reverse()method:
一旦您设法修复您的代码，请考虑使用StringBuilder而不是连接到String. 一旦你设法使用StringBuilder，你会发现方便的reverse()方法：
return new StringBuilder(backward).reverse().toString();
回答by Tomer
Your for loop is messed up, it will never run since you have the wrong condition, change it to:
你的 for 循环搞砸了，它永远不会运行，因为你有错误的条件，将其更改为：
for (int i=backward.length(); i>=0; i--)
回答by Kaleend
class Test
{
public static void main(String[] args)
{
String strtorev = "Test Code";
String newString = "";
int len = strtorev.length();
System.out.println(len);
for(int i =0;i<len;i++)
{
String subChar = strtorev.substring(strtorev.length()-1-i,strtorev.length()-i);
newString += subChar;
System.out.println(newString);
}
}
}
回答by Jayaraj Chevery
We can use recursion to reverse a String
我们可以使用递归来反转字符串
public class ReverseStringTest {
public static String reverseString(String str) {
if (str.isEmpty()) {
return str;
}
//Calling Function Recursively
return reverseString(str.substring(1)) + str.charAt(0);
}
public static void main(String[] args) {
System.out.println(reverseString("java"));
}
}
回答by Lion
You should StringBuilder. The following code should work as you expect.
你应该StringBuilder。以下代码应该按您的预期工作。
public static String ReverseStr(String backward)
{
String newString = "";
StringBuilder sb=new StringBuilder(backward);
for (int i=0; i>backward.length(); i--) //backward.length() may be replaced with sb.length()
{
String subChar = sb.charAt(i); //Replace `substring()` with `charAt()`
newString += subChar;
}
return newString;
}
回答by Its Me
public static String ReverseStr(String backward) {
String newString = "";
for (int i=backward.length()-1; i>=0; i--)
newString+ = backward.charAt(i);
return newString;
}
