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update 11. 重写 equals 方法时同时也要重写 hashcode 方法

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sjsdfg 2019-04-03 20:28:50 +08:00
parent f2e2a16d79
commit d4acbf6209
1 changed files with 3 additions and 24 deletions
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docs/notes/11. 重写equals方法时同时也要重写hashcode方法.md
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@ -12,7 +12,6 @@
```java
Map<PhoneNumber, String> m = new HashMap<>();
m.put(new PhoneNumber(707, 867, 5309), "Jenny");
```
@ -23,7 +22,6 @@ m.put(new PhoneNumber(707, 867, 5309), "Jenny");
```java
// The worst possible legal hashCode implementation - never use!
@Override public int hashCode() { return 42; }
```
@ -53,18 +51,12 @@ m.put(new PhoneNumber(707, 867, 5309), "Jenny");
```java
// Typical hashCode method
@Override
public int hashCode() {
int result = Short.hashCode(areaCode);
result = 31 * result + Short.hashCode(prefix);
result = 31 * result + Short.hashCode(lineNum);
return result;
}
```
@ -77,12 +69,9 @@ public int hashCode() {
```java
// One-line hashCode method - mediocre performance
@Override
public int hashCode() {
return Objects.hash(lineNum, prefix, areaCode);
}
```
@ -90,28 +79,18 @@ public int hashCode() {
```java
// hashCode method with lazily initialized cached hash code
private int hashCode; // Automatically initialized to 0
@Override
public int hashCode() {
int result = hashCode;
if (result == 0) {
result = Short.hashCode(areaCode);
result = 31 * result + Short.hashCode(prefix);
result = 31 * result + Short.hashCode(lineNum);
hashCode = result;
}
return result;
}
```
@ -125,4 +104,4 @@ public int hashCode() {
[1]: http://com.google.common.hash.hashing/
[1]: http://com.google.common.hash.hashing/