ArrayList basic operation and add element source code

ArrayList increase

List Implementation class of interface .

Array is used at the bottom

High query efficiency , The efficiency of addition and deletion is low , unsafe .

List<String> list=new ArrayList<>();

// Additive elements 
list.add("bjsxt");
list.add("puty");
// Note that the array index of the following addition method should not be greater than the number of existing elements 
list.add(3,"jlhh");// An error at this time 

Get elements

for(int i=0;i<list.size(),i++){
    
    sout(list.get(i));
}

Remove elements

Deletes the specified element according to the index

The return value is the value of the deleted element

String value=list.remove(1);

Replacement elements

String val=list.set(0,"ibts");

Empty the container

list.clear();

Judge whether the container is empty

list.isEmpty();

Whether to include the specified element

boolean flag=list.contains("xiaozhang");

I feel very bored here , Just skip something .

ArrayList Bottom source

AbstractList

private static final int DEFAULT_CAPACITY=10;

transienet Object[] elementData;
trasient   Data persistence   Will not be saved to disk 
    
private int size;

public ArrayList(){
    
    this.elementData=DEFAULTCAPACITY_EMPTY_ELEMENTDATA;  //{}
}

jdk1.7 Immediately load

1.8 Delay loading Empty array When to use and when to change the length of the array , Rational use of space .

add Method

The core is the last grow Method , Determine when to expand the array .

public boolean add(E e){
    
    ensureCapacityInternal(size+1);
    elementData[size++]=e;
    return true;
}

private void ensureCapacityInternal (int minCapacity){
    
    ensureExplicitCapacity(calculateCapacity(elementData,minCapacity))
}

private static int calculateCapacity(Object[] elementData,int minCapacity){
    
    if(elementData==DEFAULTCAPACITY_EMPTY_ELEMENTDATA){
    
        return Math.max(DEFAULT_CAPACITY,minCapacity);
    }
    return minCapacity;
}

private void ensureExpricitCapacity(int minCapacity){
    
    modCount++;
    
    if(minCapacity-elementData.length>0){
    
        grow(minCapacity);
    }
}

private void grow(int minCapacity){
    
    int oldCapacity=elementData.length;
    int newCapacity=oldCapacity+(oldCapacity>>1);
    if(newCapacity-minCapacity<0){
    
        newCapacity=minCapacity;
    }
    if(newCapacity-MAX_ARRAY_SIZE>0){
    
        newCapacity=hugeCapacity(minCapacity);
    }
    elementData=Arrays.copyOf(elementData,newCapacity);
}