Java小程序——字符串反转，StringBuilder与String相互转换和StringBuilder的字符串拼接

字符串反转
等于字符从后往前重新拼接
import java.util.Scanner;
/*

• 字符串反转

• */
  public class test7 {
  public static void main(String[] args) {
  Scanner sc = new Scanner(System.in);
  System.out.println(“请输入一个字符串：”);
  String a = sc.nextLine();
  String b = reverse(a);
  System.out.println(b);
  }

  public static String reverse(String a) {
  String s ="" ;
  for(int i = 0; i<a.length(); i++){
  s += a.charAt(a.length()-1 - i);
  }
  return s;
  }
  }

StringBuilder与String相互转换
import java.util.Scanner;
/*

• Stringbuild和String相互转换及StringBulid的方法
• */
  public class test8 {
  public static void main(String[] args) {
  Scanner sc = new Scanner(System.in);
  System.out.println(“请输入一个字符：”);
  String a = sc.nextLine();
  StringBuilder s = new StringBuilder(a);
  s.append(" Hello");
  s.append(" Java");
  System.out.println(s);
  s.reverse();
  String c = s.toString();
  System.out.println©;
  }
  }

StringBuilder的字符串拼接
/*

• 拼接字符串用StringBuilder
• */
  public class test9 {
  public static void main(String[] args) {
  int[] a ={2,3,4};
  StringBuilder st =new StringBuilder();
  st.append("[");
  for (int i = 0; i < a.length; i++) {
  if (i == a.length - 1) {
  st.append(a[i]);
  } else {
  st.append(a[i]);
  st.append(",");
  }
  }
  st.append("]");
  System.out.println(st);
  }
  }