【Java】【泛型】

泛型的优点
使⽤泛型有下⾯⼏个优点：
1、类型安全
2、向后兼容
3、层次清晰
4、性能较⾼，⽤GJ(泛型JAVA)编写的代码可以为java编译器和虚拟机带来更多的类型信
息，这些信息对java程序做进⼀步优化提供条件。 

import java.util.ArrayList;

/*
  栗子  了解泛型  在编译的时候检查类型安全，并且所有的强制转换都是自动和隐式的，提高代码的重用率

*/
class Cat{
    private String color;
    private int age;

    public String getColor() {
        return color;
    }

    public void setColor(String color) {
        this.color = color;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}

class Dog{
    private String name;
    private int age;

    public String getName() {
        return name;
    }

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

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}
public class test_fanxing {
    public static void main(String[] args){
        ArrayList<Dog>  al = new ArrayList<Dog>();
        ArrayList bl = new ArrayList();
        Dog dog1 = new Dog();
        al.add(dog1);
        Dog temp = al.get(0);//引用泛型后可不用强转
        Cat temp1 = (Cat)bl.get(0);
    }

}

import java.lang.reflect.Method;
import java.util.ArrayList;

/*
  栗子  反射机制  泛型的必要性

*/
class Bird{
    public void test1(){
        System.out.println("aa");
    }
    public void count(int a,int b){
        System.out.println(a+b);
    }
}
class Gen<T>{
    private T o;
    public Gen(T a){
        o = a;
    }
    public void showTypeName(){
        System.out.println("类型是： " + o.getClass().getName());
        Method [] m = o.getClass().getDeclaredMethods();
        for(int i=0;i<m.length;i++){
            System.out.println(m[i].getName());
        }
    }
}
public class test_fanxing {
    public static void main(String[] args){
        Gen<String> gen1 = new Gen<String>("aa");//<>可以放任意类型

        Gen<Bird> gen2 = new Gen<Bird>(new Bird());//<>也可以放定义好的类
        gen1.showTypeName();
        System.out.println("++++++++++++++++++++++++++++++++");
        gen2.showTypeName();

    }

}
/*
【结果】
类型是： java.lang.String
equals
toString
hashCode
compareTo
compareTo
indexOf
indexOf
indexOf
indexOf
indexOf
valueOf
valueOf
valueOf
valueOf
valueOf
valueOf
valueOf
valueOf
valueOf
charAt
checkBounds
codePointAt
codePointBefore
codePointCount
compareToIgnoreCase
concat
contains
contentEquals
contentEquals
copyValueOf
copyValueOf
endsWith
equalsIgnoreCase
format
format
getBytes
getBytes
getBytes
getBytes
getChars
getChars
hash32
indexOfSupplementary
intern
isEmpty
lastIndexOf
lastIndexOf
lastIndexOf
lastIndexOf
lastIndexOf
lastIndexOfSupplementary
length
matches
offsetByCodePoints
regionMatches
regionMatches
replace
replace
replaceAll
replaceFirst
split
split
startsWith
startsWith
subSequence
substring
substring
toCharArray
toLowerCase
toLowerCase
toUpperCase
toUpperCase
trim
++++++++++++++++++++++++++++++++
类型是： Bird
count
test1
* */