Arrayslist method

ArraysList analysis

Arrays The underlying source code actually uses arrays , The initial size is 10. The reason why values can be stored indefinitely is ： The capacity expansion mechanism in the array , When the number of arrays to be stored exceeds 10 when , It will automatically expand to save more values . The index uses ,
characteristic ： High query efficiency , The efficiency of addition and deletion is low , Thread unsafe . More use .
High query efficiency ： The method of directly using the index value of the array .
The efficiency of addition and deletion is low ： Every time you add or delete, you will have a convenience .
Thread unsafe ：（ I can't explain it at the level of Xiaobian ）
Writing a ArraysList：（ For reference only ）

public class ArraysTest<E> {
   
   private Object[] list = new Object[10];
   private int size = 0;
   public void add(E e) {

   	size++;
   	
   	for(int i =0; i < size;i++ ) {
   		
   		if(list[i] == null) {
   			list[i] = e;
   			return;
   		};
   		
   		append(e,size);
   		
   	}
   	
   }
   
   // When the size of the array is not enough, use this method to expand 
   private void append(E e,int size) {
   	
   	Object[] temp = new Object[list.length+ (list.length>>1)];
   	int i1 = 0;
   	for( ; i1<list.length;i1++) {
   		temp[i1] = list[i1];

   	}
   	list = temp;
   	list[size + 1] = e;
   }
   
   // Add a value at the specified location 
   public void add(E e,int index) {
   	
   	if(list[index] == null) {
   		size++;
   		list[index] = e; 
   	}else {
   		System.out.println("There isn't null");
   	}
   		
   	
   }
   @Override
   public String toString() {
   	System.out.print("[");
   	
   	System.out.println("[");
   	for(int i = 0;i < size-1; i++) {
   		
   		System.out.println(list[i]+",");
   		
   	}
   	
   	System.out.print(list[size-1]+"]");
   	return null;
   }
   
   // The value used to get the index position 
   public Object get(int index) {
   	
   	if(list[index] != null) {
   		return list[index];
   	}else {
   	return " I'm sorry ！ This value is not in the array ";
   	}
   }
   
   // Used to put a value at a specified position in the array 
   public void set(E e, int index) {
   	if(index <= list.length) {
   		
   		list[index] = e;
   		
   	}else if(index > list.length && index > (list.length+(list.length>>1))) {
   		
   			append(e,index);
   		
   	}else{
   		set(e,index);
   	}
   	
   	
   }
   

   
}