[Java知识库]Java字符串

Java String

java.lang.String类代表字符串。
程序当中的“”（双引号），都是String类的对象。就算没有new，也照样是。

字符串的特点

1.字符串的内容永不可变。
2.正是因为字符串不可改变，所以字符串是可以共享的。
3.字符串效果上相当于char[]字符数组，但是底层原理是byte[]字节数组。

创建方式

public String();
public String(char[] array);
public String(byte[] array);
String str = “hello”;//直接创建

一些常用方法

一些常用方法代码

//使用空参构造
        String str1 = new String();
        System.out.println("第一个字符串：" + str1);

        //根据字符数组创建字符串
        char[] charArray = {'A', 'B', 'C'};
        String str2 = new String(charArray);
        System.out.println("第二个字符串：" + str2);

        //根据字节数组创建字符串
        byte[] byteArray = {97, 98, 99};
        String str3 = new String(byteArray);
        System.out.println("第三个字符串：" + str3);

        //直接创建
        String str4 = "wenwen";
        System.out.println("第四个字符串：" + str4);

String str1 = "Hello";
        String str2 = "Hello";

        char[] charArray = {'H', 'e', 'l', 'l', 'o'};
        String str3 = new String(charArray);

        //地址比较
        System.out.println(str1 == str2);
        System.out.println(str1 == str3);

        //内容比较
        System.out.println(str1.equals(str2));
        System.out.println(str1.equals(str3));
        System.out.println("Hello".equals(str1));

        String str4 = "hello";
        System.out.println(str1.equals(str4));//false. java区分大小写
        System.out.println("============");

        String strA = "Java";
        String strB = "java";
        System.out.println(strA.equals(strB));
        System.out.println(strA.equalsIgnoreCase(strB));

		int length = "abcedjfjjafk".length();
        System.out.println("字符串的长度是：" + length);

        //拼接字符串
        String str1 = "i love ";
        String str2 = "wenwen";
        System.out.println(str1.concat(str2));

        //获取指定索引位置的单个字符
        char ch = "ilovewenwen".charAt(1);
        System.out.println("在1号索引位置的字符：" + ch);
        System.out.println("w第一次出现的位置索引：" + "ilovewenwen".indexOf("w"));

        //字符串的截取方法
        String str3 = "ilovewenwen";
        String str4 = str3.substring(5);
        System.out.println(str4);
        String str5 = str3.substring(5, 8);
        System.out.println(str5);

        //转换相关的常用方法有
        //转换为字符数组
        char[] chars = "Hello".toCharArray();
        System.out.println(chars[0]);//H
        System.out.println(chars.length);//5
        System.out.println("===========");

        //转换成为字节数组。字符串底层的字节数组
        byte[] bytes = "abc".getBytes();
        for (int i = 0; i < bytes.length; i++) {
            System.out.println(bytes[i]);
        }
        System.out.println("==========");

        //字符串的内容替换
        String str6 = "how do you do ?";
        String str7 = str6.replace("o", "*");

        System.out.println(str7);

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

        String lang1 = "fuck you";
        String lang2 = lang1.replace("fuck", "****");
        System.out.println(lang2);
        System.out.println("=========");

        //分割字符串的方法：
        String str8 = "aaa,bbb,ccc,dd";
        String[] arry1 = str8.split(",");
        for (int j = 0; j < arry1.length; j++) {
            System.out.println(arry1[j]);
        }
        System.out.println("=========");

        String str9 = "aaa bbb ccc";
        String[] arry2 = str9.split(" ");
        for (int k = 0; k < arry2.length; k++) {
            System.out.println(arry2[k]);
        }
        System.out.println("========");

        //下面的"."切割结果啥也没有
        //正确的是"\\."
        String str10 = "xxx.zzz.yyy";
        String[] arry3 = str10.split("\\.");
        System.out.println(arry3.length);//0
        for (int m = 0; m < arry3.length; m++) {
            System.out.println(arry3[m]);
        }
        System.out.println("========");

public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        System.out.println("请输入一个字符串");
        String inputStr = scan.next();

        int countUpper = 0;//大写字母
        int countLower = 0;//小写字母
        int countNumber = 0;//数字
        int countOther = 0;//其他字符

        /*//调用Charcter的方法
        char[] chars = inputStr.toCharArray();

        for (int i = 0; i < chars.length; i++) {
            if (Character.isUpperCase(chars[i])) {
                countUpper++;
            } else if (Character.isLowerCase(chars[i])) {
                countLower++;
            } else if (Character.isDigit(chars[i])) {
                countNumber++;
            } else {
                countOther++;
            }
        }*/

        //直接比较字符范围
        char[] chArray = inputStr.toCharArray();

        for (int j = 0; j < chArray.length; j++) {
            char ch = chArray[j];//当前单个字符

            if ('A' <= ch && ch <= 'Z'){
                countUpper++;
            }else  if('a'<=ch && ch <= 'z'){
                countLower++;
            }else if('0'<= ch && ch <= '9'){
                countNumber++;
            }else {
                countOther++;
            }
        }

        System.out.println("大写字母个数：" + countUpper);
        System.out.println("小写字母个数：" + countLower);
        System.out.println("数字个数：" + countNumber);
        System.out.println("其他字符个数：" + countOther);

    }