“+” Java类的运算符 [英] "+" operator for Java-classes

问题描述

我有这样的类：

 私人静态类Num {
 private int val; 
 
 public Num（int val）{
 this.val = val; 
} 
} 
  

可以添加到类的对象使用+运算符？

  Num a = new Num（18）; 
 Num b = new Num（26）; 
 Num c = a + b; 
  

解决方案

不， + 仅对数字，字符和 String 重载，并且不允许定义任何额外的重载。 p>

有一个特殊情况，当你可以连接任何对象的字符串表示 - 如果在 String 前两个操作数 toString（）在所有其他对象上调用。

  int i = 0; 
 String s =s; 
 Object o = new Object（）; 
 Foo foo = new Foo（）; 
 
 int r = i + i; // allowed 
 char c ='c'+'c'; // allowed 
 String s2 = s + s; // allowed 
 Object o2 = o + o; //不允许
 Foo foo = foo + foo; //不允许
 String s3 = s + o; //允许，调用o.toString（）并使用StringBuilder 
 String s4 = s + o + foo; // allowed 
 String s5 = o + foo; //不允许 - 没有字符串操作数
  

I have a class like this:

private static class Num {
    private int val;

    public Num(int val) {
        this.val = val;
    }
}

Is it possible to add to objects of the class by using the "+"-operator?

Num a = new Num(18);
Num b = new Num(26);
Num c = a + b;

解决方案

No, you can't. + is overloaded only for numbers, chars and String, and you are not allowed to define any additional overloadings.

There is one special case, when you can concatenate any objects' string representation - if there is a String object in the first two operands, toString() is called on all other objects.

Here's an illustration:

int i = 0;
String s = "s";
Object o = new Object();
Foo foo = new Foo();

int r = i + i; // allowed
char c = 'c' + 'c'; // allowed
String s2 = s + s; // allowed
Object o2 = o + o; // NOT allowed
Foo foo = foo + foo; // NOT allowed
String s3 = s + o; // allowed, invokes o.toString() and uses StringBuilder
String s4 = s + o + foo; // allowed
String s5 = o + foo; // NOT allowed - there's no string operand

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