1. 模拟一个trim方法，去除字符串两端的空格
package com.sggclass.string;
public class Test {
public static String newTrim (String str) {
int c = 0, d = 0;
String str1 = " ";
for (int i = 0; i < str.length(); i++) {
char a = str.charAt(i);
String b = String.valueOf(a);
if (!b.equals(str1)) {
c = i;
break;
}
}
for (int i = str.length()-1; i > 0; i--) {
char a = str.charAt(i);
String b = String.valueOf(a);
if (!b.equals(str1)) {
d = i;
break;
}
}
String result = str.substring(c, d+1);
return result;
}
public static void main(String[] args) {
String abc = newTrim(" 1 2a bc ");
System.out.println(abc);
}
}
2. 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"ab
cdefg"反转为"ab
fedcg"。
方法一
package com.sggclass.string;
public class Test {
public static String reverse (String str, int start, int end) {
String str1 = str.substring(0, start);
for (int i = end; i >= start; i--) {
str1 += str.charAt(i);
}
str1 += str.substring(end+1);
return str1;
}
public static void main(String[] args) {
String str2 = reverse("abcdefg", 2, 5);
System.out.println(str2);
}
}
方法二
package com.sggclass.string;
public class Test {
public static 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;
}
public static void main(String[] args) {
String str2 = reverse("abcdefg", 2, 5);
System.out.println(str2);
}
}
方法三
package com.sggclass.string;
public class Test {
public static String reverse (String str, int startIndex, int endIndex) {
StringBuilder str1 = new StringBuilder(str.substring(startIndex, endIndex+1));
str1.reverse();
return new String(str.substring(0, startIndex) + str1 + str.substring(endIndex+1));
}
public static void main(String[] args) {
String str2 = reverse("abcdefg", 2, 5);
System.out.println(str2);
}
}
3. 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。
package com.sggclass.string;
public class Test {
public static int find(String str1, String str2) {
int index = 0;
int count = 0;
if (str1.contains(str2)) {
while ((index = str1.indexOf(str2, index)) != -1) {
count++;
index++;
}
}
return count;
}
public static void main(String[] args) {
int i = find("abkkcadkabkebfkabkskab", "ab");
System.out.println(i);
}
}
4. 获取两个字符串中的最大相同子串（只有一个最大相同子串）。比如：str1 = “abcwerthelloyuiodef”; str2 = “cvhellobnm”; 提示：将短的字符串中长度依次递减的子串与较长的字符串进行比较
方法一：遍历所有子串，找到长度最长的相同子串。
package com.sggclass.string;
public class Test {
public static String maxSub(String str1, String str2) {
String longStr;
String shortStr;
String result = "";
//比较两个字符串哪个更长
if (str1.length() > str2.length()) {
longStr = str1;
shortStr = str2;
} else {
longStr = str2;
shortStr = str1;
}
//遍历短字符串的所有子串
for (int i = 0; i < shortStr.length(); i++) {
for (int j = i+1; j <= shortStr.length(); j++) {
String a = shortStr.substring(i, j);
//如果短字符串的子串也是长字符串的子串，且它的长度大于保存在result中的字符串的长度，就更新result
if (longStr.contains(a) && a.length() > result.length()) {
result = a;
}
}
}
return result;
}
public static void main(String[] args) {
String sub = maxSub("abcwerthelloyuiodef", "cvhellobnm");
System.out.println(sub);
}
}
方法二：从大到小遍历子串，找到的第一个相同子串即是最大相同子串。
package com.sggclass.string;
public class Test {
public static String getMaxSameString(String str1, String str2) {
//比较两个字符串哪个更长
String maxStr = (str1.length() >= str2.length()) ? str1 : str2;
String minStr = (str1.length() < str2.length()) ? str1 : str2;
int length = minStr.length();
//从大到小遍历短字符串的子串，如果它也是长字符串的子串，那它就是最大相同子串
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;
}
public static void main(String[] args) {
String sub = getMaxSameString("abcwerthelloyuiodef", "cvhellobnm");
System.out.println(sub);
}
}
如果存在多个长度相同的最大相同子串
package com.sggclass.string;
import java.util.Arrays;
public class Test {
// 如果存在多个长度相同的最大相同子串
public static String[] getMaxSameString(String str1, String str2) {
//比较两个字符串哪个更长
StringBuffer sBuffer = new StringBuffer();
String maxStr = (str1.length() >= str2.length()) ? str1 : str2;
String minStr = (str1.length() < str2.length()) ? str1 : str2;
int len = minStr.length();
//从大到小遍历短字符串的子串，如果它也是长字符串的子串，那它就是最大相同子串
for (int i = 0; i < len; i++) {
for (int x = 0, y = len - i; y <= len; x++, y++) {
String subStr = minStr.substring(x, y);
if (maxStr.contains(subStr)) {
sBuffer.append(subStr + ",");
}
}
if (sBuffer.length() != 0) {
break;
}
}
String[] split = sBuffer.toString().replaceAll(",$","").split("\,");
return split;
}
public static void main(String[] args) {
String[] sub = getMaxSameString("abcwerthelloyuiodefabcde", "cvhellobnmabcde");
System.out.println(Arrays.toString(sub));
}
}
5. 对字符串中字符进行自然顺序排序。提示：①字符串变成字符数组；②对数组排序，选择，冒泡，Array.sort();③将排序后的数组变成字符串。
package com.sggclass.string;
import java.util.Arrays;
public class Test {
public static String sort(String str) {
char[] chars = str.toCharArray();
Arrays.sort(chars);
String result = new String(chars);
return result;
}
public static void main(String[] args) {
String sorted = sort("hello123world!abc");
System.out.println(sorted);
}
}
