Java常用类-String

String篇

代码演示：

public class StringTest {
	
	@Test
	public void test2() {
		//通过字面量定义的方式：此时的s1和s2的数据JavaEE声明在方法区中的字符串常量池中
		String s1 = "JavaEE";
		String s2 = "JavaEE";
		//通过new + 构造器的方式：此时的s3和s4保存的地址值，是数据在堆空间中开辟空间以后对应的地址值
		String s3 = new String(original: "javaEE");
		String s4 = new String(original: "javaEE");

		System.out,println(s1 == s2); //true
		System.out,println(s1 == s3); //false
		System.out,println(s1 == s4); //false
		System.out,println(s3 == s4); //false

图解：

复杂题型：


常见面试题：

public class StringTest {
	String str = new String(original: "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);  //good
		System.out.println(ex.ch);   //best
	}
}

常用方法：

String与byte数组之间的转换

@Test
public void test() {
	String str1 = "abc123中国";
	byte[] bytes = str1.getBytes();   //使用默认的字符集
	System.out.println(Arrays.toString(bytes));

	byte[] gbks = str1.getBytes("gbk");  //使用gbk字符集进行编码
	System.out.println(Arrays.toString(gbks));

	System.out.println("***********");

	String str2 = new String(bytes);   //使用默认的字符集，进行解码
	System.out.println(str2);

	String str3 = new String(gbks, "gbk");
}

String与char[ ]之间的转换

@Test
public void test() {
	String str1 = "abc123";

	char[] charArray = str1.toCharArray();
	for(int i = 0 ; i < charArray.length; i++) {
		System.out.println(charArray[i]);
	}

	char[] arr = new char[]{'h','e','l','l','o'};
	String str2 = new String(arr);
	System.out.println(str2);
}

String与基本数据类型，包装类之间转换

@Test
public void test1() {
	String str1 = "123";
	//int num = (int)str1;(错误的)

	int num = Integer.parseInt(str1);
	String str2 = String.valueOf(num);  // "123"
	String str3 = num + "";

	System.out.println(str1 == str3);   //false

常见练习题

//反转
//方式一：字符数组
public String reverse(String str, int startIndex, int endIndex) {

	if(str != null && str.length() != 0) {
		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(beginIndex:0, startIndex);
		for(int i = endIndex; i >= startIndex; i--) {
			reverseStr += str.charAt(i);
		}
		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());

		builder.append(str.substring(beginIndex: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;
}

//获取“ab”在“abkkacajfanficaaifababa”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 + subStr.length());
		}
		*/

		//方式二：对方式一的改进
		while((index = mainStr.indexOf(subStr, index)) != -1) {
			count++;
			index += subLength;
		}
		return count;
	} else {
		return 0;
	}
}

//str1 = "fbakavnaiiaaiofaw"; str2 = "fafag"返回两个串中包含最大的子串
//提示：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) {
	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;
}

//改进，如果存在多个相同子串
public String getMaxSameString(String str1, String str2) {
	String maxStr = (str1.length() >= str2.length() ? str1 : str2;
	String minStr = (Str1.length() < str2.length() ? str1 : str2;
	StringBuffer sBuffer = new StringBuffer();
	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) {
				sBuffer.append(subStr + ",");
			}
		}
		if(sBuffer.length() != 0) {
			break;
		}
	}
	String[] split = sBuffer.toString().replaceAll(regex:",$", replacement: "").split(regex:"\\,");
	
	return split;
}

本文地址：https://blog.csdn.net/weixin_45990065/article/details/110183647