配列実装3スタック

public class ArrayStack {
    int stackSize=300;
    int []buffer= new int[stackSize*3];
    int []stackPointer={-1,-1,-1};
    
    void push(int stackNum,int value)
    {
        stackPointer[stackNum]++;
        int index=stackNum*stackSize+stackPointer[stackNum];
        
        buffer[index]=value;
    }
    
    int pop(int stackNum)
    {
        int index=stackNum*stackSize+stackPointer[stackNum];
        stackPointer[stackNum]--;
        int value=buffer[index];
        buffer[index]=0;
        return value;
    }
    public static void main(String[] args) {
        ArrayStack stack=new ArrayStack();
        stack.push(0, 1);
        stack.push(0, 2);
        stack.push(0, 3);
        stack.push(0, 4);
        
        System.out.println(stack.pop(0));
    }

}