String算法考察小练习（是我自己的思路，还不是最优解法）

package day2_9;

import java.util.Arrays;

/**
 * @Author Tianhao
 * @create 2021-02-09-15:05
 */
public class StringExer {



    //实现和trim()一样的作用，去掉收尾空格
    public String myTrim(String str) {

        int start = 0;
        int end = 0;
        char[] chars = str.toCharArray();
        for (int i = 0; i < chars.length; i++) {
            if (!String.valueOf(chars[i]).equals(" ")) {
                start = i;
                break;
            }
        }
        for (int i = chars.length -1; i >= 0; i--) {
            if (!String.valueOf(chars[i]).equals(" ")) {
                end = i;
                break;
            }
        }
        return str.substring(start, end + 1);
    }


    //实现数组的反转，将字符串中指定部分进行反转
    //比如“abcdef",将其中的cde反转后，输出为abedcf
    public String myReverse(String src,String target) {
        int start = src.indexOf(target);
        int end = start+target.length();
        String substring = src.substring(start, end);
        char[] chars = substring.toCharArray();
        int len = chars.length;
        char[] newChars = new char[len];
        for (int i = 0,j=len-1; i < len; i++,j--) {
            newChars[j] = chars[i];
        }
        String newS = new String(newChars);
        return src.substring(0,start)+ newS + src.substring(end);
    }


    //获取一个字符串在另一个字符串中出现的次数
    public int myContainsCount(String src,String target) {
        int count = 0;
        for (; ; ) {
            int index = src.indexOf(target);
            if (index == -1) {
                break;
            }
            count++;
            src = src.substring(index+target.length());
        }
        return count;
    }


    //获取两个字符串中最大相同子串
    public String myLongSubstring(String one, String two) {
        String max;
        String min;
        if (one.length() >= two.length()) {
            max = one;
            min = two;
        } else {
            max = two;
            min = one;
        }
        String sub;
        String targetSub = "没有相同的子串";
        int subLen = 0;
        int index;
        for (int i = 0; i < min.length(); i++) {
            for (int j = min.length(); j > i; j--) {
                sub = min.substring(i, j);
                index = max.indexOf(sub);
                if (index != -1) {
                    if (subLen < sub.length()) {
                        targetSub = sub;
                        subLen = sub.length();
                    }
                }
            }
        }
        return targetSub;
    }

    //对字符串中字符进行自然顺序排序
    public String mySort(String str) {
        char[] chars = str.toCharArray();
        Arrays.sort(chars);
        String newStr = new String(chars);
        return newStr;
    }

}

测试如下：

package day2_9;

import org.junit.Test;
import org.junit.runner.RunWith;

import java.util.Arrays;

import static org.junit.Assert.*;

/**
 * @Author Tianhao
 * @create 2021-02-09-15:12
 */

public class StringExerTest {
    StringExer stringExer = new StringExer();

    @Test
    public void myTrim() {
        String s = stringExer.myTrim("  wang tian  ");
        System.out.println(s);
    }

    @Test
    public void myReverse() {
        String s = stringExer.myReverse("helloworld", "worl");
        System.out.println(s);
    }

    @Test
    public void myContainsCount() {
        int count = stringExer.myContainsCount("xiaoqiang and xiaohong", "ng");
        System.out.println(count);

    }


    @Test
    public void myLongSubstring() {
        String target = stringExer.myLongSubstring("xiaoqiang and xiaohong", "hong is female,qiang is male.");
        System.out.println(target);

    }

    @Test
    public void mySort() {
        String str = stringExer.mySort("yienhaodlcjkf");
        System.out.println(str);
    }


    //补充知识点
    @Test
    public void test() {
        String s = "wang tian";
        char[] chars = s.toCharArray();
        //数组工具类Arrays的复制方法copyOf(xx[],newLength)
        char[] chars1 = Arrays.copyOf(chars, chars.length-3);
        System.out.println(Arrays.toString(chars));
        System.out.println(Arrays.toString(chars1));


        //基本数据类型与String的转换
        //第一种方式：String.valueOf(xxx)
        int i = 1;
        System.out.println(String.valueOf(i));
        char c = 'w';
        System.out.println(String.valueOf(c));

        //第二种方式：基本数据对应的包装类.toString()
        //下面其实也是String.valueOf(int)的内部实现
        System.out.println(Integer.toString(i));

        //对于char型，有第三种方式：
        //下面是valueOf(char)的内部实现
        char[] charArr = {c};
        String s1 = new String(charArr);
        System.out.println(s1);

    }
}