Objects and object variables

Date deadline;

• Defines an object variable deadline, It can quote Date Object of type . however , Variable deadline Not an object , In fact, there is no reference object . here , You can't put any Date Method applied to the variable .

s = deadline.toString();

• There will be compilation errors .
• So you must initialize variables first deadline

deadline = new Date();
or
deadline = birthday;	//existed object

• Reference an existing object , Will make two variables reference the same object
• An object variable does not actually contain an object , Instead, reference only one object
• stay Java in , The value of any object variable is a reference to an object stored in another place .
• new The return value of the operator is also a reference .

Date deadline = new Date();

• expression new Date() Constructed a Date Object of type , And its value is a reference to the newly created object .
• This reference is stored in the variable deadline in .