string builder

string builder:

public stringbulider:创建一个空白可变的字符串变量，不含有任何内容

public stringbulider（string str）：根据字符串的内容来创建可变字符串对象public class demo06 {

    public static void main(String[] args) {
        StringBuilder sb = new StringBuilder();
        System.out.println(sb);
        StringBuilder sc = new StringBuilder("你好");
        System.out.println(sc);
    }
}
上述为练习代码
string bulider的添加和反转

sb.append("hello").append("world").append(100);

System.out.println(sb);
sb.reverse();
System.out.println(sb);
以下是stringbulider和string的相互转换

package demo01;

public class demo07 {
    public static void main(String[] args) {
        StringBuilder sb = new StringBuilder();
        sb.append("hello");
        System.out.println(sb);
        //把stringbulider转换为string
        String s = sb.toString();
        System.out.println(s);
        //把string转换为stringbulider
        StringBuilder sc = new StringBuilder(s);
        System.out.println(sc);

    }
}

字符串的拼接

package demo01;
//字符串的拼接
public class demo08 {
    public static void main(String[] args) {
        int [] arr = {1,2,3};
        String s = add(arr);
        System.out.println(s);
    }
    public static String add(int [] arr){
        StringBuilder sb = new StringBuilder();
        sb.append("[");
        for (int i = 0; i < arr.length; i++) {
            if (i == arr.length-1){
                sb.append(arr[i]);
            }else {
                sb.append(arr[i]).append(",");
            }
        }
        sb.append("]");
       String s = sb.toString();
return s;
    }
}
字符串的反转

package demo01;

import java.util.Scanner;

public class demo09 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入你的数据：");
        String c = sc.nextLine();
        String sa = reverse(c);
        System.out.println(sa);
    }
    public static String reverse(String c){
        StringBuilder sb = new StringBuilder();
        sb.append(c);
        sb.reverse();
        String s = sb.toString();
        return s;
    }
}