Java泛型

package testSwitch;

//<T>就是定义的泛型
class Generics <T>{
    T data;
    public T getData() {
        return data;
    }
    public void setData(T data) {
        this.data = data;
    }
}

public class TestGenerics {
    public static void main(String[] args) {
        //初始化时通过<Integer>的指定类型为Integer
        Generics<Integer> genericsObject = new Generics<Integer>();
        genericsObject.setData(10);
        Integer i = genericsObject.getData();
        System.out.println(i);

    }

}

class Generics
{
    Generics()
    {
    }

   //这里把所有的T都看成了Object类型
    public Object getData()
    {
        return data;
    }
    public void setData(Object data)
    {
        this.data = data;
    }
    Object data;
}

 
public class TestGenerics
{
    public TestGenerics()
    {
    }
    public static void main(String args[])
    {
        Generics genericsObject = new Generics();
        genericsObject.setData(Integer.valueOf(10));
        //这里增加的强制类型转换
        Integer i = (Integer)genericsObject.getData();
        System.out.println(i);
    }
}

 

    //声明
    public <T> void showData(T t) {
        System.out.println(t + " and data " + data);;
    }

    //调用，直接赋值就可以了
    genericsObject.showData(20)

class Generics {
    int data;
    //限定为Number的子类
    public <T extends Number> void showData(T t) {
        System.out.println(t + " and data " + data);;
    }
}


public class TestGenerics {
    public static void main(String[] args) {
        Generics genericsObject = new Generics();
        genericsObject.showData(12.2);
    }
}

package testGenerics;
//定义原始无限定泛型
class Generics <T>{
    T data;
    public Generics(T data) {
        this.data = data;
    }

    public void showData() {
        System.out.println(data);
    }
}

class GenericsHelper{
    //在其他类中使用的时候限定泛型类型
    public static void showNewData(Generics<? extends Number> gen) {
        gen.showData();
    }
}

public class TestGenerics {
    public static void main(String[] args) {
        GenericsHelper.showNewData(new Generics<Integer>(10));
    }
}