In this book holden is struggling with issues about adulthood.
water is a symbol for adulthood.
his hunting hat is associated with holding on to childhood.
when he imagines himself as a catcher in the rye, he is disturbed by the sea of adultness. when you enter in and become a part of the mass.
so if you want to enter in adulthood you have obey the rules of aduthood. or else you will be looked upon as odd.
holden feels. if he gives into "growing up" then he will lose himself. this book finds him torn between holding on to childhood and stepping into adulthood.
situations in life like getting in trouble at school, dealing with his sisters death, are making him decide if hes ready to grow up.