设计模式之单例模式

单例模式的一种实现

将类的所有构造方法都设为private让其无法从外部实例化，然后再内部来实例化一个类，提供一个get方法获取。

public class Student {
    private String name;
    private String id;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    private Student(String name, String id) {
        this.name = name;
        this.id = id;
    }

    private Student() {
    }

    @Override
    public String toString() {
        return "Student [name=" + name + ", id=" + id + "]";
    }

    private static Student instance = null;

    public static Student getInstance() {//判断是否存在实例
        if (instance == null)
            instance = new Student();
        return instance;
    }
}

测试：

Student student1 = Student.getInstance();//先获取一个学生对象
student1.setId("9527");
student1.setName("华安");
Student student2 = Student.getInstance();//再获取学一个学生对象
System.out.println(student1==student2);
System.out.println(student2);