JAVA 攻城狮第十三天-优快云博客

本文链接：https://blog.youkuaiyun.com/PolarAurora/article/details/74977890

今天算是正式的暑假的第一天
然后今天早上起床很晚然后起床之后还没有吃早饭把宿舍小小的整理一下
然后去了实验室开始看java 没有看视频看的是Java的书
看类和方法这块觉得看的不是很懂就先跳过了然后看的String类
下面会总结一下String类的构造方法

package StringDemo;
//String类的构造方法详解
//方法一：**String();**
//方法二：**String(byte[] bytes)**
//方法三：**String (byte[] bytes,int index,int length)**
//方法四：**String（char[] value）**
//方法五：**String（char[] value,int index,int length）**
//方法六：**String（String str）**
public class StringDemo1 {

    public static void main(String[] args) {
        //方法一：String();
        String s1=new String();
        //String这个类重写了Object父类的方法，return this；
        System.out.println("s1:"+s1);
        System.out.println("s1.length:"+s1.length());
        System.out.println("---------------------");

        //方法二：String(byte[] bytes)
        byte[] byts={97,98,99,100,101,102};
        String s2=new String(byts);
        System.out.println("s2:"+s2);
        System.out.println("s2.length:"+s2.length());
        System.out.println("---------------------");

        //方法三：String (byte[] bytes,int index,int length)
        byte[] byts2={97,98,99,100,101,102};
        String s3=new String(byts2,2,4);
        System.out.println("s3:"+s3);
        System.out.println("s3.length:"+s3.length());
        System.out.println("---------------------");

        //方法四：String（char[] value）
        char [] value={'a','b','c','d','e','f'};
        String s4=new String(value);
        System.out.println("s4:"+s4);
        System.out.println("s4.length:"+s4.length());
        System.out.println("---------------------");

        //方法五：String（char[] value,int index,int length）
        char [] value2={'a','b','c','d','e','f'};
        String s5=new String(value,2,4);
        System.out.println("s5:"+s5);
        System.out.println("s5.length:"+s5.length());
        System.out.println("---------------------");

        //方法六：String（String str）
        String s6=new String("abcdef");
        System.out.println("s6:"+s6);
        System.out.println("s6.length:"+s6.length());
        System.out.println("---------------------");

    }

}

然后学习了关于String类的一些方法

1.length()
  Return the length of the string.
  The length is equal to the number of 16-bit Unicode characters in the string.

  public class demo{
     public static void main(String[] args) {
        String str1 = "Are you a student?";
        int n1 = str1.length();
    }
  }

2.substring method
  原型：public String substring(int beginindex,int endindex);
        public String substring(int beginindex);

  public class demo2{
    public static void main(String[] args) {
        String str = "Are you a student?";
        String str1 = str.substring(4,8);
        String str2 = str.substring(8);
    }
  }


3.equals method
   原型：public boolean equals(Object anObject)

   public class demo3{
    public static void main(String[] args) {
        String str1 = "Are you a student?";
        String str2 = "Are you A student?";
        int n1 = str1.equals(str2);  //false
    }
   }

4.indexOf method
   原型：public int indexOf(int ch);//from the beginning;
         public itn indexOf(int ch,int fromindenx);//from the fromindex;

   public class demo4{
    public static void main(String[] args) {
        String str1 = "Are you a student?";
        int n1 = indexOf('e');
        int n2 = indexOf('e',5);
    }
   }

5.compareTo method
   原型：public int compareTo(String anotherstring)

   public class demo5{
    public static void main(String[] args) {
        String str1 = "Are you a student?";
        String str2 = "Are you A student?";
        int n1 = str1.compareTo(str2);

    }
   }

6.replace method
   原型：public String replace (char oldchar,char newchar);

   public class demo6{
    public static void main(String[] args) {
        String str1 = "Are you a student?";
        String str2 = str1.replace('s','t');
    }
   }

7.trim() method
   String str1.trim();
   用于删除字符串开头和结尾的空格.

8.startsWith & endsWith 

   原型：public boolean startsWith(String prefix,int toffset);
         public boolean endsWith(String suffix);

   用处：String str1 = "Are you a student?";
         int n1 = str1.startsWith("you",4);
         从第四个开始检测子字符串是否和参数相同 返回布尔值
         int n2 = str1.endsWith("dent"); 
         从最后开始检查子字符串是否和参数相同 返回布尔值