1. 表示本类的属性  this.name = name;

2. 调用本类的普通方法：this.方法();

3. 调用本类构造方法：this();

• this(); 要放在构造方法的行首，不能放在普通方法中。
• 构造方法使用this()相互调用时，至少保留一个构造方法没有调用其他构造方法。

 4. this 表示当前对象

class Staff{	private int ID;	private String name;	private int salary;	private String department;		Staff(){}		Staff(int ID){		this(ID,"Noname",0,"No");	}		Staff(int ID, String name){		this(ID,name,1000,"Back");	}		Staff(int ID, String name, int salary, String department){		this.ID = ID;		this.name = name;		this.salary = salary;		this.department = department;	}		String getInfo() {		return "ID: "+this.ID+"\nName: "+this.name+"\nSalary: "+this.salary+"\nDepartment: "+this.department;	}		void print() {		System.out.println("当前对象为："+this);	}}public class TestThis {	public static void main(String[] args) {		// TODO Auto-generated method stub		Staff s1 = new Staff();		Staff s2 = new Staff(100);		Staff s3 = new Staff(50,"Tom");		Staff s4 = new Staff(111,"Jack",10000,"Finance");		System.out.println(s1.getInfo());		System.out.println(s2.getInfo());		System.out.println(s3.getInfo());		System.out.println(s4.getInfo());				System.out.println(s1);		s1.print();	}}