重温经典《Thinking in java》第四版之第五章 初始化与清理（二十七）

“5.2 方法重载”这一小节一上来讲了一个取名字的问题，放在计算机编程语言里面，就是相同的名字的方法或者函数可以表达多种不同的含义，他们被“重载”了。下面直接举一个包含构造器重载和普通方法重载的例子，更直观的对“重载”有个理解：

importstaticnet.mindview.util.Print.*; 
classTree { 
intheight; 
Tree() { 
print("Planting a seedling"); 
height=0; 
    } 
Tree(intinitialHeight) { 
height=initialHeight; 
print("Creating new Tree that is "+height+" feet tall"); 
    } 
voidinfo() { 
print("Tree is "+height+" feet tall"); 
    } 
voidinfo(Strings) { 
print(s+": Tree is "+height+" feet tall"); 
    } 
} 
publicclassOverloading { 
publicstaticvoidmain(String[] args) { 
for(inti=0; i<5; i++) { 
Treet=newTree(i); 
t.info(); 
t.info("overloaded method"); 
        } 
// Overloaded constructor: newTree(); 
    } 
}

/* Output:

Creating new Tree that is 0 feet tall

Tree is 0 feet tall

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 seedling

*///:~

创建Tree对象时，即可以不含参数，也可以用树的高度当参数。对于普通的方法也是一样的道理，info()是不显示额外的信息，inf(String)则可以显示额外的信息。你还可以定义更多的重载函数，比如info(String,String)等等。从这些直观的代码可以总结出一个规律：相同名字的方法，每个重载的方法都必须有独一无二参数类型列表。从这个规律大家是不是就明白了什么是重载，不用过多的去追求文字上的定义描述了。

下面提到了一种情况就是，虽然参数顺序的不同也足以区分两个方法，不过，一般不建议这么做，因为这么做没什么意义，更增加了代码的维护难度：

importstaticnet.mindview.util.Print.*; 
publicclassOverloadingOrder { 
staticvoidf(Strings, inti) { 
print("String: "+s+", int: "+i); 
    } 
staticvoidf(inti, Strings) { 
print("int: "+i+", String: "+s); 
    } 
publicstaticvoidmain(String[] args) { 
f("String first", 11); 
f(99, "Int first"); 
    } 
}

/* Output:

String: String first, int: 11

int: 99, String: Int first

*///:~