java基础第4课

work018.java

package test01;


public class work018
{


  public static void main(String[] args)
  {
    String str1 = "";
    long startTime = System.currentTimeMillis();
    for (int i = 0; i < 10000; i++)
    {
      str1 = str1 + i;
    }
    long endTime = System.currentTimeMillis();
    long time = endTime - startTime;
    System.out.println("String消耗时间：" + time);

    StringBuilder builder = new StringBuilder("");
    long startTime2 = System.currentTimeMillis();
    for (int j = 0; j < 10000; j++)
    {
      builder.append(j);
    }
    long endTime2 = System.currentTimeMillis();
    long time2 = endTime2 - startTime2;
    System.out.println("StringBuilder消耗时间：" + time2);

    StringBuilder builder2 = new StringBuilder("hello");
    builder2.insert(5, " world");
    System.out.println(builder2.toString());

    StringBuilder builder3 = new StringBuilder("abcdefghijklmnopqrstuvwxyz");
    builder3.delete(4, 25);
    System.out.println(builder3.toString());


  }


}

work019.java

package test01;


public class work019
{


  public static void main(String[] args)
  {
    //
    String str1 = "Where are you come from";
    String str2 = str1.toUpperCase();
    String str3 = str2.toLowerCase();
    System.out.println(str1);
    System.out.println(str2);
    System.out.println(str3);

    //
    String str4 = "I have money";
    String str5 = "you have money";
    String str6 = str4.substring(7, 12);
    String str7 = str5.substring(9);
    System.out.println(str4);
    System.out.println(str5);
    System.out.println(str6);
    System.out.println(str7);
    if(str6.equalsIgnoreCase(str7))
    {
      System.out.println("两个子串相同");
    }
    else 
    {
      System.out.println("两个子串不相同");
    }

    //
    String str8 = "13830008001";
    String regString = "\\d{11}";
    if (str8.matches(regString))
    {
      System.out.println(str8 + "是合法的手机号码");
    }
    String str9 = "13909005002";
    String regString2 = "^1[3-9]\\d{9}$"; //^开始位置，$结束位置
    if (str9.matches(regString2))
    {
      System.out.println(str9 + "是合法的手机号码");
    }

    //
    StringBuilder builder = new StringBuilder();
    for (int j = 0; j < 10; j++)
    {
      builder.append(j);
    }
    System.out.println(builder.toString());


  }


}

work020.java

package test01;


public class work020
{


  public static void main(String[] args)
  {
    int[] arr = new int[5];
    for (int i = 0; i < arr.length; i++)
    {
      arr[i] = i + 1;
      System.out.print(arr[i]);
    }
    System.out.println();

    int arr2[] = new int[5];
    for (int j = 0; j < arr2.length; j++)
    {
      arr2[j] = j + 1;
      System.out.print(arr2[j]);
    }
    System.out.println();

    int[] arr3 = {1,2,3,4,5};
    for (int k = 0; k < arr3.length; k++)
    {
      System.out.print(arr3[k]);
    }
    System.out.println();

    int[] day = new int[]{31,28,31,30,31,30,31,31,30,31,30,31};
    for (int m = 0; m < day.length; m++)
    {
      System.out.println((m + 1) + "月有" +day[m] + "天");
    }


  }


}

work021.java

package test02;


public class work021
{


  public static void main(String[] args)
  {
    int myArr[][];
    myArr = new int[2][4];
    myArr[0][1] = 11;

    int myArr1[][] = new int[2][];
    myArr1[0] = new int[2];
    myArr1[1] = new int[3];
    myArr1[0][1] = 11;
    myArr1[1][2] = 22;

    int myArr2[][] = {{12,0},{45,10}};
    System.out.println(myArr2[1][0]);

    int a[][] = new int[3][4];
    for (int i = 0; i < a.length; i++)
    {
      for (int j = 0; j < a[i].length; j++)
      {
        System.out.print(a[i][j] + " ");
      }
      System.out.println();
    }
  }


}