pass by value vs pass by reference
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pass by value
当参数是pass by value时,调用者和被调用者是有两个相同具有相同值的独立变量,被调用者修改了参数的值,调用者是看不到效果的。
pass by reference
当参数是pass by reference时,调用者和被调用者是使用一个相同的变量,如果调用者更改了参数的值,调用者是可以看到效果的。
Java参数传递
java都是pass by value, 看下面这个例子
public static void main(String[] args) { String x = new String("ab"); change(x); System.out.println(x); //ab}public static void change(String x) { x = "cd";}
这个例子和string的不可变性无关,只是因为Java是值传递
看另外一个例子
public static void main( String[] args ) { Dog aDog = new Dog("Max"); foo(aDog); // when foo(...) returns, the name of the dog has been changed to "Fifi" aDog.getName().equals("Fifi"); // true}public static void foo(Dog d) { d.getName().equals("Max"); // true // this changes the name of d to be "Fifi" d.setName("Fifi");}
这个表面一看看起来是传递的引用,实际上,Dog aDog是个变量,这个变量存储的是对象new Dog(“Max”)的地址,参数传递的时候传递的仍然是aDog的值,只是这个sDog的值又恰好是new Dog(“Max”)的地址而已。
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