面试题

public class StringTest {String str = new String("good");char[] ch = { 't', 'e', 's', 't' };public void change(String str, char ch[]) {str = "test ok";ch[0] = 'b';}public static void main(String[] args) {StringTest ex = new StringTest();ex.change(ex.str, ex.ch);System.out.println(ex.str);//goodSystem.out.println(ex.ch);//best}
}

练习题1

将一个字符串进行反转。将字符串中指定部分进行反转。比如“abcdefg”反转为”abfedcg”。

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) {//第一部分String reverseStr = str.substring(0, startIndex);//第二部分for (int i = endIndex; i >= startIndex; i--) {reverseStr += str.charAt(i);}//第三部分reverseStr += str.substring(endIndex + 1);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());//第一部分builder.append(str.substring(0, startIndex));//第二部分for (int i = endIndex; i >= startIndex; i--) {builder.append(str.charAt(i));}//第三部分builder.append(str.substring(endIndex + 1));return builder.toString();
}

练习题2

获取一个字符串在另一个字符串中出现的次数。比如：获取“ ab”在 “abkkcadkabkebfkabkskab” 中出现的次数。

public int getCount(String mainStr, String subStr) {int mainLength = mainStr.length();int subLength = subStr.length();int count = 0;int index = 0;if (mainLength >= subLength) {//方式一：
//            while((index = mainStr.indexOf(subStr)) != -1) {
//                count++;
//                mainStr = mainStr.substring(index + subLength);
//            }//方式二：对方式一的改进while ((index = mainStr.indexOf(subStr, index)) != -1) {count++;index += subLength;}}return count;}

练习题3

获取两个字符串中最大相同子串。（两个字符串中只有一个最大相同子串）比如：str1 = "abcwerthelloyuiodef“;str2 = “cvhellobnm”。

//将短的那个串进行长度依次递减的子串与较长的串比较。
public String getMaxSameString(String str1, String str2) {if(str1 != null && str2 != null) {String maxStr = (str1.length() >= str2.length()) ? str1 : str2;String minStr = (str1.length() < str2.length()) ? str1 : str2;int length = minStr.length();for (int i = 0; i < length; i++) {for (int x = 0, y = length - i; y <= length; x++, y++) {String subStr = minStr.substring(x, y);if (maxStr.contains(subStr)) {return subStr;}}}}return null;}