Java 和最终初始化

Question

我正在从 .NET“转换”为 Java。我想知道为什么下面的代码不起作用

class MyClass{
  private final int intVar;  //ok
  private final Paint paint; //error "Variable paint might not have been initialized"

  public MyClass(){
       intVar = 12; 
       initializePaint(); 
  }

  private void initializePaint(){
       paint = new Paint();  //error  "cannot assign a variable to final variable"
  }

}

Answer 1

您应该在类或构造函数中声明的位置初始化最终字段。

构造函数中允许初始化final字段，因为构造函数在对象创建时只被调用一次。

当您在方法 initializePaint() 中初始化它时，您将收到编译器错误，因为该方法可以多次调用，并且最终变量/字段是常量且无法更改。因为您将多次调用 initializePaint() 方法，多次初始化最终字段，这是错误的。因此编译器会给出错误。

class MyClass{
  private final int intVar;  //ok
  private final Paint paint;// paint = new Paint(); to avoid //error "Variable paint might not have been initialized"

  public MyClass(){
       intVar = 12; 
       //initializePaint(); 
       paint = new Paint(); // here initialized And allowed.
  }

  private void initializePaint(){
       paint = new Paint();  //error  "cannot assign a variable to final variable"
  }
}