5.2 方法重载

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1. 区分重载方法
2. 涉及基本类型的重载
3. 以返回值区分重载方法

• 重载(overload):相同的此何以表达不同的含义
• 方法重载:让方法名相同而形参不同的构造器同时存在,同时尽管方法重载是构造器所必须的,但它亦可用于其他方法,而且用法同样方便

//：initialization/Overloading.java
//Demonstration of both constructor
//and ordinary method overloading

class Tree{
    int height;
    Tree(){
        System.out.println("Planting a seeding");
        height=0;
    }

    Tree(int initialHeight){
        height=initialHeight;
        System.out.println("Creating new Tree that is "+height+" feet tall");
    }

    void info(){
       System.out.println("Tree is "+ height + " feet tall");
    }

    void info(String s){
        System.out.println(s+" :Tree is "+height+" feet tall");
    }
}

public class Overloading{
    public static void main(String[] args){
        for(int i=0;i<5;i++){
            Tree t=new Tree(i);
            t.info();
            t.info("overloaded method");
        }
        new Tree();//Overloaded constructor
    }
}/*output:
overloaded method :Tree is 0 feet tall
Creating new Tree that is 1 feet tall
Tree is 1 feet tall
overloaded method :Tree is 1 feet tall
Creating new Tree that is 2 feet tall
Tree is 2 feet tall
overloaded method :Tree is 2 feet tall
Creating new Tree that is 3 feet tall
Tree is 3 feet tall
overloaded method :Tree is 3 feet tall
Creating new Tree that is 4 feet tall
Tree is 4 feet tall
overloaded method :Tree is 4 feet tall
Planting a seeding
*///:~

5.2.1 区分重载方法

• 每个重载方法都必须有一个独一无二的参数列表

  • 甚至参数顺序的不同也可以区分两个方法,但是这样会使代码难以维护

    //:initialization/OverloadingOrder.java
    //Overloading based on the order of the arguments
    public class OverloadingOrder{
        static void f(String s,int i){
            System.out.println("String: "+s+" ,int: "+i);
        }
        static void f(int i,String s){
            System.out.println("int: "+i+"String: "+s);
        }
    
        public static void main(String[] args){
            f("String first",11);
            f(99,"Integer first");
        }
    }/*output:
    String: String first ,int: 11
    int: 99String: Integer first
    *///:~
    

    

5.2.2 涉及基本类型的重载

• 如果传入的数据类型小于方法中声明的形参类型,实际数据类型就会被提升
• 如果传入的实际参数大于重载方法声明的形参,就得通过类型转换来进行窄化处理

5.2.3 以返回值区分重载方法

• 行不通

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