Question

我认为我的语法有问题。所以请帮我解释一下这些语法：

public class Main { 

  public static void main(String arg[]) { 
    String number = "1234";
    System.out.println("original String: " + number);
    String reversed = inPlaceReverse(number);
    System.out.println("reversed String: " + reversed); 
  } 

  public  String inPlaceReverse(final String input) {
    final StringBuilder builder = new StringBuilder(input); 
    int length = builder.length();
    for (int i = 0; i < length / 2; i++) { 
      final char current = builder.charAt(i);
      final int otherEnd = length - i - 1;
      builder.setCharAt(i, .charAt(otherEnd)); // swap 
      builder.setCharAt(otherEnd, current); 
    }
    return builder.toString(); 
  }

}

反向功能无法正常工作。

Answer 1

StringBuilder具有执行此操作的功能：

StringBuilder.reverse()您还可以将.toString（）附加到此调用以将其恢复为字符串。

https://docs.oracle.com/javase/7/docs/api/java/lang/StringBuilder.html#reverse()

Answer 2

您的代码中存在一些错误。

1）error: illegal start of expression builder.setCharAt(i, .charAt(otherEnd));

更正：builder.setCharAt(i, **builder**.charAt(otherEnd));

2）error: non-static method inPlaceReverse(String) cannot be referenced from a static context

这是因为你已经将main（）声明为静态，而你的isPlaceReverse（）是非静态的。您不能在静态成员中引用非静态成员。

将您的功能定义更改为public **static** String inPlaceReverse(final String input)

完成上述更正后，您将获得所需的输出：

public class Main {

    public static void main(String args[]) {

        String number = "1234";
        System.out.println("original String: " + number);
        String reversed = inPlaceReverse(number);
        System.out.println("reversed String: " + reversed);
    }


    public static String inPlaceReverse(final String input) {
        final StringBuilder builder = new StringBuilder(input);
        int length = builder.length();
        for (int i = 0; i < length / 2; i++) {
            final char current = builder.charAt(i);
            final int otherEnd = length - i - 1;
            builder.setCharAt(i, builder.charAt(otherEnd)); // swap
            builder.setCharAt(otherEnd, current);
        }

        return builder.toString();
    }
}

输出原始字符串：1234 反向字符串：4321

Answer 3

将您的反向逻辑更新为：

public static  String inPlaceReverse(final String input) {
            final StringBuilder builder = new StringBuilder(input); 
            int length = builder.length();
            for (int i = 0; i < length / 2; i++) { 
                final char current = builder.charAt(i);
                final char otherEnd = builder.charAt(length - i - 1);
                builder.setCharAt(i, otherEnd); // swap 
                builder.setCharAt(length-i-1, current); 
           }
            return builder.toString(); 
}

更合适的方式是：

 public static String inPlaceReverse(final String input) { // make it static
                final StringBuilder builder = new StringBuilder(input);
                return builder.reverse().toString();
 }

反转字符串，代码无法正常工作

3 个答案: