OCP - 1
Classes, Desing Patterns, Principles, Generics and Collections
Classes, Desing Patterns, Principles, Generics and Collections
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Kartei Details
| Karten | 124 |
|---|---|
| Sprache | English |
| Kategorie | Informatik |
| Stufe | Andere |
| Erstellt / Aktualisiert | 31.01.2019 / 08.01.2020 |
| Lizenzierung | Keine Angabe |
| Weblink |
https://card2brain.ch/box/20190131_ocp_1
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| Einbinden |
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What is the Result of `null instanceOf X` ?
False, an instanceOf check with null always results in false
When are instanceOf checks executed?
- For Classes: At Compiletime
- For Interfaces: At Runtime
What is virtual method invocation?
It basically means that Jva will look at subclasses when finding the right method to call (override)
What's the goal of @override?
It is helpful because the compiler can tell you when you've messd up
What does the equals signature look like?
public boolean equals(Object obj)
What is the equals contract?
- "Should not change at random"
- reflexive: x.equals(x) == true
- symmetric: x.equals(y) == y.equals(x)
- transitive: x.equals(y) == y.equals(z) == z.equals(x)
- consistent: x.equals(y) == x.equals(y) (does not change when x and y are not modified)
- An object an null are not equal
- x.equals(null) must return false
What is the contract of hashCode?
- The result must not change -> derive it from members that do not change (eg. an id)
- The hasCode() can use a subset of equals
- two equal objects must return the same hashcode
- the hash code can be a constant, altough it is not efficient
What does the hashCode signature look like?
public int hashCode()
