Java：String、StringBuilder、reverse反转、append拼接、遍历、统计

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import java.util.Scanner;

/*
* Scanner:用于获取键盘录入数据
* public String nextline():获取键盘录入字符串数据
*/

public class ScannerLearn {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入数据：");
        String line = sc.nextLine();
        System.out.println("您输入的数据是："+line);

/*
* String构造方法
* public String（） 创建空白字符串对象
* public String（char[] chs） 根据字符数组的内容，来创建字符串对象
* public String（byte[] bys） 根据字节数组的内容，来创建字符串对象
* String s = "abc" 直接赋值（推荐使用）*/
        String s1 = new String();
        System.out.println("s1："+s1);  //s1：

        char [] chs = {'a','b','c'};
        String s2 = new String(chs);
        System.out.println("s2："+s2); //s2：abc

        byte[] bys = {97,98,99};  //97字节底层对应的就是a
        String s3 = new String(bys);
        System.out.println("s3："+s3); //s3：abc

        //以下存储内存地址不一样
        String s4 = new String(chs);
        String s5 = new String(chs);

        //以下存储内存地址一样
        String s6 = "abc";
        String s7 = "abc";

        //比较的为地址值
        System.out.println(s4==s5); //false
        System.out.println(s6==s7); //true
        System.out.println(s4==s6); //false

        //比较数据值
        System.out.println(s4.equals(s5)); //true
        System.out.println(s6.equals(s7)); //true
        System.out.println(s4.equals(s6)); //true

        //遍历字符串
        String name = "YinRuMin";
        for(int i=0;i<name.length();i++){
            System.out.println(name.charAt(i));
        }

        //统计字符次数，大小写和数字分别统计
        //Scanner ss = new Scanner(System.in);
        System.out.println("请输入字符串：");
        String word = sc.nextLine();
        int uw = 0;
        int lw = 0;
        int dig = 0;
        for(int i=0;i<word.length();i++){
            if(word.charAt(i)>='A'&&word.charAt(i)<='Z'){
                uw+=1;
            }else if(word.charAt(i)>='a'&&word.charAt(i)<='z'){
                lw+=1;
            }else if(word.charAt(i)>='0'&&word.charAt(i)<='9'){
                dig+=1;
            }
        }
        System.out.println("大写字母有："+uw+"个");
        System.out.println("小写字母有："+lw+"个");
        System.out.println("数字字符有："+dig+"个");

        //StringBuild
        StringBuilder sb = new StringBuilder();
        System.out.println("sb:"+sb);
        System.out.println("sb.length():"+sb.length());

        StringBuilder sb2 = new StringBuilder("abdcdd");
        System.out.println("sb2:"+sb2);
        System.out.println("sb2.length():"+sb2.length());

        StringBuilder sb3 = sb2.append("eee");
        System.out.println("sb2:"+sb2); //sb2:abdcddeee
        System.out.println("sb3:"+sb3); //sb2:abdcddeee
        System.out.println(sb2==sb3);  //true

        sb.append(100);
        sb.append("yin");
        sb.append("xxx");
        System.out.println("sb:"+sb); //sb:100yinxxx
        sb.append(22).append("ccc").append("fff"); //链式拼接
        System.out.println("sb:"+sb); //sb:100yinxxx22cccfff

        sb.reverse();  //反转
        System.out.println("sb:"+sb); //sb:fffccc22xxxniy001

        //String转换为StringBuilder
        String sb6 = "Iverson";
        StringBuilder sb7 = new StringBuilder(sb6);
        System.out.println("sb7:"+sb7);

        //StringBuilder转换为String
        StringBuilder sb4 = new StringBuilder();
        sb4.append("Iverson");
        //String sb5 = sb4;错误方法
        String sb5 = sb4.toString();
        System.out.println("sb5:"+sb5);


        //拼接字符串
        int[] arr = {1,2,3,4,5,6};
        String s = arrayToString(arr);  //普通拼接
        System.out.println("s:"+s); //s:[1, 2, 3, 4, 5, 6]
        String sb8 = arrayToString2(arr); //StringBuilder拼接
        System.out.println("sb8:"+sb8); //sb8:[1,2,3,4,5,6]
    }
    public static String arrayToString(int[] arr){
        String s = "";
        s +="[";
        for(int i = 0;i<arr.length;i++){
            if (i==arr.length-1){
                s+=arr[i];
            }else {
                s+=arr[i];
                s+=", ";
            }
        }
        s+="]";
        return s;
    }

    public static String arrayToString2(int[] arr){
        StringBuilder s = new StringBuilder();
        s.append("[");
        for(int i = 0;i<arr.length;i++){
            if (i==arr.length-1){
                s.append(arr[i]);
            }else {
                s.append(arr[i]).append(",");
            }
        }
        s.append("]");
        String sb = s.toString();
        return sb;
    }
}

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