展示代码比谈论它更容易。我还在互联网上搜索了答案,但找不到任何答案,所以这是我的代码:
我还添加了一个输出,位于第 50-70 行。 61-70 的输出是“正确”的,也是我想要的。
我使用 fill() 方法是错误的还是什么?我无法理解这个...
真的有区别吗?
ClassB[][] classB_2Array = new ClassB[10][10];
在此之间:
for (ClassB[] classB_1Array : classB_2Array) {
Arrays.fill(classB_1Array, new ClassB());
}
对此:
for (int i = 0; i < classB_2Array.length; i++) {
for (int j = 0; j < classB_2Array[0].length; j++) {
classB_2Array[i][j] = new ClassB();
}
}
无论如何,请查看我的代码并感谢大家的回答!
最佳答案
回答您的问题:是的,有区别(请参阅 JavaDoc)。
您的第一个版本将一个对象实例放入一行的每个数组元素中。因此,对此实例的更改在数组同一行中的每个元素中都是可见的。您总共将拥有 i
个 ClassB
个实例。
第二个版本将自己的实例放入每个数组元素中。您总共将拥有 i*j
ClassB
个实例。
您的代码的第一个版本相当于
for (ClassB[] classB_1Array : classB_2Array) {
ClassB instance = new ClassB();
Arrays.fill(classB_1Array, instance);
}
希望这些信息对您有所帮助,我没有查看您的pastebin代码。
编辑:
为了澄清您的误解,请仔细查看该程序的输出:
import java.util.Arrays;
public class ArrayFiller {
public static void main(String[] args) {
// your first version:
Person[][] yourFirstVersion = new Person[2][2];
for (Person[] array : yourFirstVersion) {
Arrays.fill(array, new Person("Mike"));
}
System.out.println(Arrays.deepToString(yourFirstVersion));
yourFirstVersion[0][1].setName("Paul");
System.out.println(Arrays.deepToString(yourFirstVersion));
System.out.println("-----");
// equivalent: my version:
Person[][] myVersion = new Person[2][2];
for (Person[] array : myVersion) {
Person person = new Person("John");
Arrays.fill(array, person);
}
System.out.println(Arrays.deepToString(myVersion));
myVersion[0][1].setName("Thomas");
System.out.println(Arrays.deepToString(myVersion));
System.out.println("-----");
// your second version
Person[][] yourSecondVersion = new Person[2][2];
for (int i = 0; i < yourSecondVersion.length; i++) {
for (int j = 0; j < yourSecondVersion[i].length; j++) {
yourSecondVersion[i][j] = new Person("Max");
}
}
System.out.println(Arrays.deepToString(yourSecondVersion));
yourSecondVersion[0][1].setName("Chris");
System.out.println(Arrays.deepToString(yourSecondVersion));
}
private static class Person {
private String name;
public Person(String name) {
System.out.println("Constructor called for " + name);
this.name = name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return name;
}
}
}
这是输出:
Constructor called for Mike
Constructor called for Mike
[[Mike, Mike], [Mike, Mike]]
[[Paul, Paul], [Mike, Mike]]
-----
Constructor called for John
Constructor called for John
[[John, John], [John, John]]
[[Thomas, Thomas], [John, John]]
-----
Constructor called for Max
Constructor called for Max
Constructor called for Max
Constructor called for Max
[[Max, Max], [Max, Max]]
[[Max, Chris], [Max, Max]]
关于java - 如何使用 fill() 方法填充 Java 中特定对象的多维数组?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/14093685/