一个无法执行if语句问题

import java.util.*;
class Square
{
    int length,xTopLeft,yTopLeft,xBottomRight,yBottomRight;
    int ID;
    static int nextID;
    Square(int xTopLeft,int yTopLeft,int length)
    {
        ID=nextID;nextID++;
        this.length=length;this.xTopLeft=xTopLeft;this.yTopLeft=yTopLeft;
        xBottomRight=xTopLeft+length;yBottomRight=yTopLeft-length;
    }
    void Move(int xOffset,int yOffset)
    {
        xTopLeft=xTopLeft+xOffset;
        yTopLeft=yTopLeft+yOffset;
        xBottomRight=xBottomRight+xOffset;
        yBottomRight=yBottomRight+yOffset;
    }
    double Area()
    {
        return length*length;
    }
    double Perimeter()
    {
        return length*4;
    }
   
}
public class SquareExp {
    public static void main(String[] args)
    {
        Scanner scanner=new Scanner(System.in);
        int length;
        System.out.print("请输入你的边长:");
        length=scanner.nextInt();
        System.out.print("请输入你的左上角顶点x:");
        int x=scanner.nextInt();
        System.out.print("请输入你的左上角顶点y:");
        int y=scanner.nextInt();
        Square square=new Square(x,y,length);
        System.out.println("输入: Y移动矩形  N不移动矩形");
        String a=scanner.nextLine();
        if(a=="Y")
        {
            System.out.print("请输入你移动的x距离:");
            int xOffset=scanner.nextInt();
            System.out.print("请输入你移动的y距离:");
            int yOffset=scanner.nextInt();
            square.Move(xOffset,yOffset);
        }
        else
        {   
        }
        System.out.println("边长="+length+" 周长="+square.Perimeter()+" 面积="+square.Area());
        System.out.print("左上顶点的坐标为:("+square.xTopLeft+","+square.yTopLeft+") ");
        System.out.println("右下顶点的坐标为:("+square.xBottomRight+","+square.yBottomRight+")");
    }
}
为什么没办法执行if语句，用if(a.quealsIgnoreCase("Y"))也不可以