Java--字符串笔记

• 字符串的常量池

• 字符串相关的比较方法
  

public class Demo01String {
    public static void main(String[] args) {
        String s1 = "Java";
        String s2 ="java";
        System.out.println(s1.equalsIgnoreCase(s2));//true 忽略大小写
        System.out.println(s1.equals(s2));//false 区分大小写
    }
}

• 字符串的获取

public class Demo01String {
    public static void main(String[] args) {
        int length = "ssdfdffdfdfdfdfdfdfd".length();
        System.out.println("字符串长度"+length);

        String s1 = "hello";
        String s2 = "world";
        String s3 = s1.concat(s2);
        System.out.println(s3); //helloworld

        char ch = s1.charAt(1);
        System.out.println("s1的1号索引位置的字符是"+ch); //e

        System.out.println(s1.indexOf("aaa")); //-1 返回aaa第一次索引的位置，因为没有所以返回-1
        System.out.println(s1.indexOf("el"));  //1
        System.out.println("abcabc".indexOf("ca"));//2


    }
}

• 字符串的分割

package com.qml.study;

public class Demo02String {
    public static void main(String[] args) {
        String string = "aaa,bbb,vvvv";
        String[] arry = string.split(",");
        for (int i = 0; i < arry.length; i++) {
            System.out.println(arry[i]);  //aaa 换行bbb 换行vvv

        }

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

        String string2 = "aaa.bbb.ccc";
        String[] str2 = string2.split("\\.");   //split用.分割记得带\\.
        for (int i = 0; i < str2.length; i++) {
            System.out.println(str2[i]);
        }


    }
}

/*把数组{1,2,3} 打印出字符串 [a1#a2#a3]

• */

package com.qml.study;
/*把数组{1,2,3} 打印出字符串 [a1#a2#a3]
* */
public class Demo03String {
    public static void main(String[] args) {
     int[] array = {1,2,3};
     System.out.println( func(array));    //[a1#a2#a3]
    }

    public static String func(int[] array){
        String string1 = "[";
        for (int i = 0; i < array.length; i++) {
            if (i == array.length-1){
                string1 += "a"+array[i]+"]";
            }
            else {
                string1 += "a"+array[i]+"#";
            }

        }
        return string1;
    }


}

/**

• 键盘输入一个字符串，并统计各类字符出现的次数。
• 种类：大写字母，小写字母，数字，其他
  */

package com.qml.study;

import java.util.Scanner;

/**
 * 键盘输入一个字符串，并统计各个字符出现的次数。
 * 种类：大写字母，小写字母，数字，其他
 */

public class Demo04String {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入：");
        String string = scanner.next();

        int contUpper = 0 ;
        int contLower = 0;
        int contNum = 0;
        int other = 0;

        char[] chars = string.toCharArray();
        for (int i = 0; i < chars.length; i++) {
            char ch = chars[i];
            if ('A' <= ch && ch <= 'Z')
            {contUpper++;
            }else if ('a'<= ch && ch <='z'){
                contLower++;
            }
            else if('0' <= ch && ch <= '9'){
                contNum++;
            }
            else {other++;}
        }
        System.out.println(contUpper);
        System.out.println(contLower);
        System.out.println(contNum);
        System.out.println(other);
    }
}