Second week of Java learning (2)

array

The Concept of Container

Store multiple data together, and each data is called a container element.

// Water cup, wardrobe, classroom

Array: A container that stores a fixed length and guarantees a uniform type of all elements

Arrays are objects

Definition of arrays

1. Static binding

2. Dynamic binding

private static void guokexun() { 
    //array
    int a=10; 
    //static state    
    int[] arr={1, 2, 3};    
    System.out.println(arr[0]);    
    //dynamic    
    int[] arr1=new int[5];    
    System.out.println(arr1[0]);    
    arr1[0]=1;    
    //The third way of definition is static binding    
    int[] arr2=new int[]{1, 2, 3};    
    int[] arr3={2, 0, 1 ,9, 8, 8};    
    Arrays.sort(arr3);
    //Ranking from small to large    
    System.out.println("Sorted arrays");    
    for (int i:arr3){        
       System.out.println(i);    
   }
}

Arrays are reference data types

private static void demo2() {    
    String s1="guo";    
    System.out.println(s1);    
    int[] arr1={1 ,2 ,3};    
    Person n1=new Person();    
    System.out.println(n1);
}

Inheritance of arrays

Object is a superclass of all classes

Special cases:

Array types can be converted upwards to Object [], but the real parent class is actually Object.

private static void demo3() {    
    String[] s1=new String[5];    
    //Upward transformation    
    Object o=s1;    
    Object[] o1=new Object[5];                           System.out.println(s1.getClass().getSuperclass().getName());    
    Object[] o2=s1;
}

Enhanced for cycle

private static void demo4() {    
    int[] arr={12,22,11,99};    
    for (int i=0;i<4;i++){        
        System.out.println(arr[i]+"  ");    
    }    
    System.out.println();    
    for (int i:arr){//Shortcut key iter        
        System.out.print(i+"   ");    
    }
}

Queries for Maximum and Minimum Values

private static void demo5() {    
    int[] arr={99,22,77,1,55};    
    int max=0;    
    int min=arr[0];    
    for (int i : arr) {        
        if (i>max)            
                max=i;    
    }    
    for (int i : arr) {        
        if (i<min)            
                min=i;    
    }    
    System.out.println("The maximum value is"+max);    
    System.out.println("The minimum value is"+min);
}

Array exchange order

private static void demo6() {    
    int[] arr={33,21,45,22,13};    
    for (int min=0,max=arr.length-1;min<=max;min++,max--){        
        int temp=arr[min];        
        arr[min]=arr[max];        
        arr[max]=temp;    
    }    
    for (int i : arr) {        
        System.out.println(i);    
    }
}

Digital memory

private static void demo7() {    
    int i=1;    
    i=i++;   //i + + assigns value first in operation, such as a=i + +, assigns a=i first, then i=i+1, so the result is a==1 
    int j=i++;    
    int k=i+ ++i*i++; //+ + I first calculates the assignment, such as a=++i, first calculates i=i+1, then assigns a=i, so the result is a==2 
    System.out.println(i+" "+j+" "+k);//i=4 j=1 k=11
}