java.util.NoSuchElementException：没有值存在 Java 8 Lambda
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/31011091/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
java.util.NoSuchElementException: No value present Java 8 Lambda
提问by Alexandre Picard-Lemieux
I got this. But my list is not empty and they have element with code "ADPL". Why this return me NoSuchElement ?
我懂了。但我的列表不是空的，他们有代码“ADPL”的元素。为什么这会返回给我 NoSuchElement ？
String retour = CodeExecutionChaine.A.getCode();
if (!lstChaines.isEmpty()) {
retour = lstChaines.stream()
.filter(t -> t.getNomChaine() == Chaines.ADPL.getCode())
.map(Chaine::getStatutChaine)
.findFirst()
.orElse(CodeExecutionChaine.A.getCode());
The enum Chaines
枚举链
public enum Chaines {
ADPL("ADPL"),
ADIL("ADIL"),
ADSL("ADSL");
private String code = "";
Chaines(String code) {
this.code = code;
}
public String getCode() {
return this.code;
}
}
This is the same for CodeExecutionChaine
这与 CodeExecutionChaine 相同
采纳答案by CKing
Change t -> t.getNomChaine() == Chaines.ADPL.getCode()to t -> t.equals(Chaines.ADPL.getCode()).
更改t -> t.getNomChaine() == Chaines.ADPL.getCode()为t -> t.equals(Chaines.ADPL.getCode())。
==checks for identity. Therefore, ==will result into trueonly if two references point to the same object. On the other hand, equalschecks for equality. Two references that don't point to the same object but have similar propertiesare still considered equal. You get a NoSuchElementExceptionbecause you used ==to filteryour Streamwhich resulted in zero elements satisfying the condition.
==检查身份。因此，只有当两个引用指向同一个对象时==才会导致true。另一方面，equals检查equality. 不指向同一个对象但具有相似对象的两个引用properties仍然被认为是相等的。你得到了NoSuchElementException，因为你使用==到filter你Stream这就造成了满足条件的零个元素。
