您正在阴影变量：
public Hra1()
{
// the following variable's *scope* is inside of this constructor only
// outside of the constructor, the local variable below doesn't exist.
Mince [] poleMinci = new Mince[20];
poleMinci[0] = new Mince("st?íbrná", "coin.png");
poleMinci[3] = new Mince("st?íbrná", "coin.png");
poleMinci[4] = new Mince("zlatá", "coin_gold.png");
poleMinci[8] = new Mince("st?íbrná", "coin.png");
poleMinci[10] = new Mince("st?íbrná", "coin.png");
poleMinci[12] = new Mince("st?íbrná", "coin.png");
}
在该构造函数中，由于poleMinci是在构造函数内部声明的，因此仅在构造函数内部可见。如果您在类中具有相同名称的变量，则该变量将为null。要解决此问题，请不要在本地重新声明该变量。做：
public Hra1()
{
// Mince [] poleMinci = new Mince[20]; // **** not this ****
poleMinci = new Mince[20]; // **** but this. note the difference? ****
poleMinci[0] = new Mince("st?íbrná", "coin.png");
poleMinci[3] = new Mince("st?íbrná", "coin.png");
poleMinci[4] = new Mince("zlatá", "coin_gold.png");
poleMinci[8] = new Mince("st?íbrná", "coin.png");
poleMinci[10] = new Mince("st?íbrná", "coin.png");
poleMinci[12] = new Mince("st?íbrná", "coin.png");
}
有关此问题的更多信息，请查看Variable Shadowing。大多数IDE都会警告您您可能正在执行此操作，或者设置了允许他们执行此操作的设置。我使用Eclipse并将IDE设置为警告我。您可能也希望这样做。
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