Arrays

1. Array creation

//Create Array
		int array[] = new int[3];

1. Assigning values to elements in an array

//Assigning values to elements in an array
		array[0] = 1;
		array[1] = 2;
		array[2] = 3;

1. Assigning values to arrays at creation time

//Create an array and assign values
   	int array[] = new int[] {1,2,3};

1. All elements in the output array

System.out.println (Arrays.toString (target array));

1. Add a new element after the array

public class OpArrayTest {    //Addition of Array Elements
	public static void main(String[] args) {
		
		//Create an array and assign values
		int array[] = new int[] {1,2,3};
		System.out.println(Arrays.toString(array));
		
		//Data to be added
		int dext = 4;
		
		//Create a new array of length + 1 of the original array
		int array1[] = new int[array.length+1];
		
		//Assign elements of the original array to the new array
		for(int i=0;i<array.length;i++) {
			array1[i] = array[i];
		}
		
		//Add a new element to the end of a new array
		array1[array.length] = dext;
		
		//New Array Replace Old Array
		array=array1;
		System.out.println(Arrays.toString(array));
	}

1. Delete elements from the array

package shuzu;

import java.util.Arrays;

public class OpArrayTest2 {     //Deletion of array elements
	public static void main(String[] args) {
		
		//Create an array and assign values to it
		int array[] = new int[] {1,2,3,4,5};
		System.out.println(Arrays.toString(array));
		
		//Subscripts of array elements need to be removed
		int dext = 2;
		
		//Create a new array length is how long the array length is -1
		int array1[] = new int[array.length-1];
		
		//Assign elements from the original array to the new array, except those that need to be deleted
		for(int i=0;i<array1.length;i++) {
			//judge
			if(i<dext) {
				array1[i] = array[i];
			}else {
				array1[i] = array[i+1];
			}
			
		}
		
		//New Array Replace Old Array
		array = array1;
		System.out.println(Arrays.toString(array));
	}

}

2. Object-oriented arrays

1. Create a tool class, MyArray.java, to encapsulate some methods of an array of operations.

package shuzu.util;

import java.util.Arrays;

public class MyArray {
	
	//Same as an array of stored data
	private int array[];
	
	public MyArray() {
		array = new int[0];
	}
	
	//Get the length of the array
	public int size() {
		return array.length;
	}
	
	//Print Output Array
	public void show() {
		System.out.println(Arrays.toString(array));
	}
	
	//Add elements to the array
	public void add(int dex) {
		
		//Create a new array of length + 1
		int array1[] = new int[array.length+1];
		
		//Copy elements from the original array into the new array
		for(int i=0;i<array.length;i++) {
			array1[i] = array[i];
		}
		
		//Add a new element after a new array
		array1[array.length] = dex;
		
		//New Array Replace Old Array
		array = array1;
		
	}
	
	//Delete elements from the array
	public void delete(int dex) {
		
		//Create a new array, length is principle, array length -1
		int array1[] = new int[array.length-1];
		
		//Copy elements from the original array into the new array except those to be deleted
		if(dex<0||dex>array.length-1) {
			throw new RuntimeException("subscript out of range");
		}
		for(int i=0;i<array1.length;i++) {
			if(i<dex) {
				array1[i] = array[i];
			}else {
				array1[i] = array[i+1];
			}
		}
		
		//New Array Replace Old Array
		array = array1;
	}
	
	//Insert an element to the location specified by the array
	public void insert(int dex,int nex) {    //dex:Specify the location nex:for the element that needs to be inserted
		
		//Create a new array of length + 1
		int array1[] = new int[array.length+1];
		
		//Copy elements from the original array into the new array
		if(dex<0||dex>array.length-1) {
			throw new RuntimeException("subscript out of range");
		}
		for(int i=0;i<array.length;i++) {
			//judge
			if(i<dex) {
				array1[i] = array[i];
			}else {
				array1[i+1] = array[i];
			}
			
		}
		
		//Insert a new element
		array1[dex]  = nex;
		//New Array Replaces Old Array
		array = array1;
		
	}
	
	//Replace elements at specified locations
	public void set(int dex ,int nex) {    //dex: Subscript nex of the element to be replaced: Replaced element

		//Replace elements,
		array[dex] = nex;
		
		
		
		
	}

}

1. Write a test class to create a variable array and add, delete, replace, output, and so on.

package shuzu;

import shuzu.util.MyArray;

public class MyArrayTest {
	public static void main(String[] args) {
		
		//Create a variable array
		MyArray ma = new MyArray();
		
		//Array of output
		ma.show();
		
		//Add an element to the array
		ma.add(1);
		ma.add(66);
		ma.show();
		
		//Delete an element from the array
		ma.add(2);
		ma.show();
		ma.add(3);
		ma.add(4);
		ma.add(5);
		ma.show();
		ma.delete(2);
		ma.show();
		
		//Add elements at specified locations
		ma.insert(2, 8);
		ma.show();
		
		//Replace elements at specified locations
		ma.set(2, 11);
		ma.show();
	}

}

1. The console effect is as follows:
   

3. Linear Search

1. Creates a target array, compares the target element to each element in the array, and returns its subscript if it is equal

package shuzu;

public class SearchTest {     //Linear Find Target Elements
	public static void main(String[] ages) {
		
		//Create Target Array
		int array[] = new int[] {1,3,2,9,6,8};
		
		//Target element of lookup
		int dex = 8;
		
		//Subscript of target element
		int nex = -1;
		
		for(int i=0;i<array.length;i++) {
			if(array[i] == dex) {
				nex = i;
				break;
			}
		}
		
		//Print target element subscript
		System.out.println("Subscript of target element:"+nex);
	
	}

}

4. Binary Search

1. Create an ordered array and assign values to it, recording where you start, center, and end.Each time the loop compares that intermediate element with the target element, if the intermediate element is larger than the target element, the end position becomes the position of the previous element of the intermediate element.If the middle element is smaller than the target element, the start position becomes the position of the next element after the middle element.

package shuzu;

import java.util.Arrays;

public class BinaryTest {
	public static void main(String[] ages) {
		
		//Create Target Array
		int array[] = new int[] {1,3,2,4,5,6,7,8,9};
		Arrays.sort(array);
		System.out.println(Arrays.toString(array));
		
		//Target Element
		int nex = 7;
		
		//Record start position
		int begin = 0;
		
		//Record End Position
		int end = array.length-1;
		
		//Record middle position
		int mid = (begin+end)/2;
		
		//Record Target Location
		int dex = -1;
		
		while(true) {
			//Determine if the middle element is the one to look for
			if(array[mid] == nex) {
				dex = mid;
				break;
			}else {
				if(array[mid]>nex) {    //The intermediate element is larger than the target element
					end = mid-1;        //Change the end position to the previous element of the intermediate element
				}else {                 //The middle element is smaller than the target element
					begin = mid+1;      //Change the position of the start element to the next position of the intermediate element
				}
			}
			mid = (begin+end)/2;        //New intermediate elements
		}
		System.out.println("Find the location of the target element"+dex);
		
		
	}
	
	//Output the location of the target element found
	
	

}