第二章 基本数据类型 ，数组 和枚举类型

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public class Example2_1 {
     public static void main (String args[]){
         char ch1='w',ch2='好';
         int p1=32831,p2=30452;
         System.out.println("""+ch1+""的位置:"+(int)ch1);
         System.out.println("""+ch2+""的位置:"+(int)ch2);  
         System.out.println("第"+p1+"个位置上的字符是:"+(char)p1);                             
         System.out.println("第"+p2+"个位置上的字符是:"+(char)p2);  
     }
 } 

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public class Example2_2 {
    public static void main (String args[]) {
       byte b =22;
       int n =129;
       float f =123456.6789f ;
       double d=123456789.123456789;
       System.out.println("b= "+b);
       System.out.println("n= "+n); 
       System.out.println("f= "+f);   
       System.out.println("d= "+d);   
       b=(byte)n;                                   //导致精度的损失
       f=(float)d;                                  //导致精度的损失
       System.out.println("b= "+b); 
       System.out.println("f= "+f); 
    }
}

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import java.util.Scanner;
public class Example2_3 {
    public static void main (String args[]){
        System.out.println("用空格(或回车)做分隔,输入若干个数,最后输入#结束,n然后回车确认.");
        Scanner reader=new Scanner(System.in);
        double sum=0;
        int m = 0;
        while(reader.hasNextDouble()){
        double x = reader.nextDouble();
        m =m + 1;
        sum = sum + x;
      }
      System.out.println(m +"个数的和为"+sum); 
      System.out.println(m +"个数的平均值"+sum/m);
     }
} 
       
        

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public class Example2_4 {
    public static void main(String args[]){
        int a[]={1,2,3,4};
        int b[]={100,200,300}；
        System.out. println("数组 a 的元素个数="+ a.length);
        System. out. println("数组 b的元素个数="+ b.length)；
        System.out.println("数组a的引用="+a);
        System.out.println("数组 b 的引用="+b);
        System. out. printin("a == b 的结果是"+(a== b));
        a= b;
        System.out. println("数组 a 的元素个数="+ a.length)；
        System.out. println("数组 b 的元素个数="+ b.length)；
        System.out.println("a== b的结果是"+(a == b))；
        System.out.println("a[0]="+a[o]+",a[1]="+a[1]+",a[2]="+ a[2]);
        System.out.print("b[0]="+a[0]+",b[1]="+b[1]+",b[2]="+b[2]);
    }
}

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import java.util.Arrays;
public class Example2_5 {
    public static void main(String args[]){
        char [] a = {'a','b','c','d','e','f'},
                   b ={'1','2','3','4','5','6'}; 
        int [] c= {1,2,3,4,5,6},
                  d = {10,20,30,40,50,60};
        System.arraycopy(a, 0, b, O, a.length);
        System.arraycopy(c, 2, d, 2, c.length-3);
        System. out. println("数组 a 的各个元素中的值:");
        System.out.println(Arrays.toString(a));
        System.out. println("数组 b 的各个元素中的值:")；
        System.out.println(Arrays.toString(b));
        System.out.println("数组 c 的各个元素中的值:");
        System.out.println(Arrays.toString(c));
        System.out.println("数组 d 的各个元素中的值:")；
        System.out. println(Arrays.toString(d)); 
     }
}

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import java.util.*;
public class Example2_6 {
    public static void main(String args[]){
        int []a ={10,20,30,40,50,60},b,c,d;
        b= Arrays.copyof(a,10)；
        System. out. println("数组 a 的各个元素中的值:");
        System.out.println(Arrays.toString(a));
        System. out. println("数组 b 的各个元素中的值:")；
        System.out. println(Arrays. toString(b))；
        c=Arrays.copyOfRange(a,3,5);
        System. out. println("数组 c 的各个元素中的值:")；
        System. out. println(Arrays.toString(c))；
        d= Arrays.copyOfRange(a,3,9)；
        System. out. println("数组 d 的各个元素中的值:");
        System.out.println(Arrays.toString(d));
    }
}

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import java.util.Arrays;
public class Example2_7 {
    public static void main(String args[]){
        int [] a = {12,34,45,6,45,90,123,19,34};
        Arrays.sort(a);
        System.out.println(Arrays.toString(a));
        int number=45;
        int index= Arrays.binarySearch(a,number);
        if(index>=0){
            System.out.println(number+"和数组中索引为"+index+"的元素相同");
        }
        else{
            System.out.println(number+"不与数组中任何元素值相同");
        }
    }
}

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import java.util.Scanner;
    enum Season {
        春季,夏季,秋季,冬季
    }
    public class Example2_8 {
        public static void main(String args[]){
            Season x = null;
            Scanner reader=new Scanner(System.in);
            int n = reader.nextInt();
            if (n == 1)
                x = Season.春季;
            else if(n == 2)
                x = Season.夏季;
            else if(n == 3)
                x = Season.秋季;
            else if(n == 4)
                x = Season.冬季;
            System.out.println("现在是"+x);
        }
}

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public class Example2_9 {
    public static void main(String args[]){
        Weekday x= Weekday.星期日;
        if(x==Weekday.星期日){
            System.out.println(x);
            System.out.println("今天我休息");
        }
    }
}