java单例模式 的饿汉式和懒汉式代码实现

package day10_9;

// 单例模式 饿汉式	
public class Singleton {

	public static void main(String[] args) {
		Student s1 = Student.getStudent();
		Student s2 = Student.getStudent();
		System.out.println(s1 == s2);

		Teacher t1 = Teacher.getTeacher();
		Teacher t2 = Teacher.getTeacher();

		System.out.println(t1 == t2);

	}

}

// 饿汉式
class Student {

	private Student() {

	}

	private static Student student = new Student();

	public static Student getStudent() {
		return student;
	}

}

// 懒汉式
class Teacher {

	private Teacher() {

	}

	private static Teacher teacher = null;

	public static Teacher getTeacher() {
		if (teacher == null) {
			teacher = new Teacher();
		}
		return teacher;

	}

}