Summary of Java Generics Example Tutorial

Generics are a very important knowledge point in Java. Generics are widely used in the Java collection class framework. In this article, we will look at the Java generic

Automobile class from scratch:

public class Automobile {    private String name;    public Automobile(String name){        this.name= name;
    }    public String getName() {        return name;
    }    public void setName(String name) {        this.name = name;
    }
}

Holder1 class: holds a specified single type object.

public class Holder1 {    private Automobile automobile;    public Holder1(Automobile automobile){        this.automobile = automobile;
    }    public Automobile get(){        return this.automobile;
    }
}

Holder2 class: holds Object object.

public class Holder2 {    private Object object;    public Holder2(Object object){        this.setObject(object);
    }    public Object getObject() {        return object;
    }    public void setObject(Object object) {        this.object = object;
    }
}

Holder3 class: Use generics to hold a single object, but do not specify its type for the time being, and decide what kind of object to hold when using it.

public class Holder3 <T>{    private T t;    public Holder3(T t){        this.setT(t);
    }    public T getT() {        return t;
    }    public void setT(T t) {        this.t = t;
    }
}

Main program Main:

public class Main {    public static void main(String[] args) {        /*使用Holder1*/
        Holder1 holder1 = new Holder1(new Automobile("Iphone"));
        System.out.println(holder1.get().getName());        
        /*使用Holder2*/
        //使holder2持有String类型对象
        Holder2 holder2 = new Holder2("XiaoMi");
        System.out.println(holder2.getObject()); 
        //更改holder2中持有的对象类型
        holder2.setObject(new Automobile("HuaWei"));        //向下转型Object->Automobile
        Automobile automobile = (Automobile) holder2.getObject();
        System.out.println(automobile.getName());        
        /*使用Holder3*/
        //告诉编译器holder3持有的对象类型为String        //此时holder3拥有的对象类型只能为String，不能变更
        Holder3<String> holder3 = new Holder3<String>("Vivo");
        System.out.println(holder3.getT());        //告诉编译器anotherHolder3持有的对象类型为Automobile        //此时anotherHolder3拥有的对象类型只能为Automobile，不能变更
        Holder3<Automobile> anotherHolder3 = new Holder3<Automobile>(new Automobile("Oneplus"));
        System.out.println(anotherHolder3.getT().getName());
    }    
}

The program running result is:

Iphone
XiaoMi
HuaWei
Vivo
Oneplus

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