字符串部分翻转

package com.learning.java;

import org.junit.Test;

public class StringDemo {

    //方式一：转换为char[]
    public String reverse(String str, int startIndex, int endIndex) {
        if (str != null) {
            char[] arr = str.toCharArray();
            for (int x = startIndex, y = endIndex; x < y; x++, y--) {
                char temp = arr[x];
                arr[x] = arr[y];
                arr[y] = temp;
            }
            return new String(arr);
        }
        return null;
    }

    //方式二：使用String的拼接
    public String reverse1(String str, int startIndex, int endIndex) {
        if (str != null) {
            String reverseStr = str.substring(0, startIndex);

            for (int i = endIndex; i >= startIndex; i--) {
                reverseStr += str.charAt(i);
            }
            reverseStr += str.substring(endIndex + 1, str.length());
            return reverseStr;
        }
        return null;
    }

    //方式三：使用StringBuffer/StringBuilder替换String
    public String reverse2(String str, int startIndex, int endIndex) {
        if (str != null) {
            StringBuilder builder = new StringBuilder(str.length());
            builder.append(str.substring(0, startIndex));
            for (int i = endIndex; i >= startIndex; i--) {
                builder.append(str.charAt(i));
            }
            builder.append(str.substring(endIndex + 1));
            return builder.toString();
        }
        return null;
    }

    @Test
    public void test1() {
        String str = "abcdefg";
        String str1 = reverse(str, 2, 5);
        String str2 = reverse1(str, 2, 5);
        String str3 = reverse2(str, 2, 5);

        System.out.println(str1);
        System.out.println(str2);
        System.out.println(str3);

    }
}