字符串基础

package zifuchuan;

import java.util.Date;

public class dsd {

    public static void main(String[] args) {
    
        //字符串
        
        String str = "aa 醉了";   //字符串双引号       常用
        
           char c = 'c';             //字符单引号
                
         int j =1;
         
         String str1 = new String ("a c bc bc f");   //少用
         
         //连接字符 串    +
         
         System.out.println("str+str1+j=" +str+str1+j);  
         
         //99乘法表 
         
         int []a= new int [5];
         
         int l = a. length;  // 不带括号是属性
         
        int g =str1.length();    //带括号是方法
        
        System.out.println("str1.length()=" +g);
        
        //查找
        int sy =str1.indexOf("bc");
        
        System.out.println("str1.indexOf(\"bc\") =" +sy);
        
        int sy1 =str1.lastIndexOf("bc");
        
        System.out.println("str1.indexOf(\"bc\") =" +sy1);
        
        //取出字符
        
      System.out.println("charAt=" + str1.charAt(2));
      
     //截取字符串
      
      System.out.println("substring= " +str1.substring(3));
      System.out.println("substring= " +str1.substring(3,5));  //索引值5结束
      
      //字符串的去除空格
      
      String str3 = "  abc def gh  ";
      
      System.out.println("str3.trim()=#" + str3.trim() + "#");//去空格
      
      
      str3 = str3.trim();//保存去空格
 
      System.out.println("str3.trim()=#" + str3 + "#");
      
      //替换
      
      str3 = str3.replace(" ","");
      
      System.out.println("str3.replace()=#" + str3 + "#");
      
      str3=str3.replace("bc","BC");
      
      System.out.println("str3.replace()=#" + str3 + "#");
      
      //判断字符串开始
      
      System.out.println("str3.startsWith() =" +str3.startsWith("a"));
      System.out.println("str3.endsWith() =" +str3.endsWith("a"));
      
      String a1 = new String ("aaa");
      String a2 = new String ("Aaa");
      System.out.println("a1==a2="+a1==a2);        //==比较的是内存地址即a1与a2,不是各自包含的字符串
      
      a1.equals(a2);
      
      System.out.println("a1.equals(a2)=" +a1.equals(a2));// 区分大小写
      System.out.println("a1.equalsIgnoreCase(a2)=" +a1.equalsIgnoreCase(a2));//不区分大小写
      
      String b1 = "aaa";
      String b2 = "aaa";
      System.out.println("b1==b2="+(b1==b2));   //不建议使用

      //按字典顺序比较  Unicode的值
      
      System.out.println("compareTo=" +a1.compareTo(a2));//从第一位开始比较
      
      //大小写转换
      
      System.out.println("a1.toUpperCase=" +a1.toUpperCase());//转换大写
      System.out.println("a1.toLowerCase=" +a1.toLowerCase());//转换小写
      
      //字符串分割   
      
      String fg = "aa;bb;cc,ccc;ddd.ss";
      
      String [] arr= fg.split(";");
      String [] arr2 = fg.split(";|,");
      String [] arr1 = fg.split(";" , 2 );
      
      for (String f :arr)
      {
          System.out.println(f);
          
      }
      
      //格式化字符串  日期时间
      // String.format(格式符,要被格式化的对象 );
      
      Date dt =new Date();    //实例化日期，生成当前日期
      
      System.out.println(String.format("%tF",dt));
      
      System.out.println(String.format("%tT",dt));
      
      System.out.println(String.format("%tR",dt));
      
      System.out.println(String.format("%tF",dt)+" "+String.format("%tT",dt));
      
      System.out.println("200的十六进制="+String.format("%x",200));
      
      System.out.println("特定换行"+ String.format("%n")+"换行");
      
      System.out.println("特定换行"+ "\n"+"换行");
      
      StringBuilder strb = new  StringBuilder();
      
      strb.append("abc");
      strb.append("def");
      strb.append("ghr");
      
      strb.insert(2,"$$");
      strb.delete(2, 5);
      System.out.println("strb = " + strb.toString());
      
      
      
      
      
      
      
    
      
      
      
        
    
         

         
         
    }

}