英文:
Enhanced for loop and Array
问题
以下是代码的翻译部分：
public class modifyALelements {
public static void main(String[] args) {
StringBuilder myArr [] = {new StringBuilder("One"), new StringBuilder("Two")};
for (StringBuilder val: myArr)
System.out.println(val);
for (StringBuilder val: myArr)
val.append("Way");
for (StringBuilder val: myArr)
System.out.println(val);
StringBuilder anotherArr[] = { new StringBuilder("Java"), new StringBuilder("Loop") };
for (StringBuilder element : anotherArr)
System.out.println(element);
for (StringBuilder element : anotherArr)
element = new StringBuilder("Test");
for (StringBuilder element : anotherArr)
System.out.println(element);
}
}
输出：
One
Two
OneWay
TwoWay
Java
Loop
Java
Loop
请注意，另一个数组（anotherArr）中的值在最后两个for-each循环中没有更改为"Test"，这是因为在这些循环中，你只是修改了元素的引用，而没有修改元素本身。要修改元素的内容，你需要使用append()等方法，就像你在第一个数组（myArr）中所做的那样。
英文:
public class modifyALelements {
public static void main(String[] args) {
StringBuilder myArr [] = {new StringBuilder("One"), new StringBuilder("Two")};
for (StringBuilder val: myArr)
System.out.println(val);
for (StringBuilder val: myArr)
val.append("Way");
for (StringBuilder val: myArr)
System.out.println(val);
StringBuilder anotherArr[] = { new StringBuilder("Java"), new StringBuilder("Loop") };
for (StringBuilder element : anotherArr)
System.out.println(element);
for (StringBuilder element : anotherArr)
element = new StringBuilder("Test");
for (StringBuilder element : anotherArr)
System.out.println(element);
}
}
output:
One
Two
OneWay
TwoWay
Java
Loop
Java
Loop
Hi all,
Can someone please explain why has values of anotherArr not changed to Test last two for-each loops. When you use append() method, changes are applied e.g. OneWay and TwoWay.
Many thanks.
答案1
得分: 1
在Java中，类类型是引用类型。这意味着类型为 StringBuilder 的变量将保存对 StringBuilder 对象的引用。
for (StringBuilder val : myArr)
val.append("Way");
在这里，我们从 myArr 中获取引用。然后我们调用 append 方法，它会修改所引用的对象。
for (StringBuilder element : anotherArr)
element = new StringBuilder("Test");
在这里，我们同样从数组中获取引用。然而，然后我们重新分配了一个变量。这仅仅改变了 element 变量引用的对象，实际上没有改变任何对象。
英文:
In java, class types are reference types. This means that a variable of type StringBuilder will hold a reference to a StringBuilder object.
for (StringBuilder val: myArr)
val.append("Way");
Here we take references from myArr. Then we call method append, which changes the referred object.
for (StringBuilder element : anotherArr)
element = new StringBuilder("Test");
Here we also take a reference from an array. However, then we reassign a variable. This only changes what element variable refers to. No object is actually changed.
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