【每日日报】第四十天 工具类

1 今天看网课

1）StingBuilder和StringJoiner

package liuer;
import java.util.StringJoiner;

public class StringBuilderDemo {
    public static void main(String[] args){
        StringBuilder sb=new StringBuilder();
        sb.append(52);
        sb.append(1).append("中国");
        System.out.println(sb.toString());
        int[] arr=new int[]{12,24,35,46};
        StringJoiner sj=new StringJoiner(", ","[","]");
        for(int x:arr){
            sj.add(Integer.toString(x));
        }
        System.out.println(sj.toString());
    }
}

2)Intege

package liuer;

public class IntegerDemo {
    public static void main(String[] args){
        Integer a=12;
        System.out.print(a.valueOf(a));
    }

}

3)Math

package liuer;
import java.util.Random;

public class MathDemo {
      public static void main(String[] args){
          Random random=new Random();
          for(int i=0;i<10;i++){
              System.out.println(random.nextInt(10));
          }
      }

}

2 没什么问题

3 明天继续看网课