有没有一种方法可以确保在编译时设置不可变对象中的某些字段,同时保持参数的角色清晰?
我正在尝试创建不可变对象的方法。以下构建器对象 非常有吸引力,因为它们清楚地表明了论点的作用。不过我想 使用编译器验证某些字段是否已设置,例如使用 Immutable()
构造函数调用。 StrictImmutableBuilder
提供这些检查,但相当嘈杂。有没有办法以 LaxImmutableBuilder 的形式获得相同的检查?也许使用注释?
public class Immutable {
public static void main(String[] args) {
new Immutable("13272873C", 23, false);
// nice but what where those arguments?
new LaxImmutableBuilder() {{
refCode("13272873C");
age(23);
subscribed(false);
}}.build();
// now I know what each value represents
// but what if I forgot to set one?
new StrictImmutableBuilder() {
public String refCode() { return "13272873C"; }
public int age() { return 23; }
public boolean subscribed() { return false; }
}.build();
// now I'm forced to set each field, but now
// we have the extra noise of "return"
// and also "public" if we want to use
// this outside the current package
// is there another way? maybe using annotations?
}
private final String refCode;
private final int age;
private final boolean subscribed;
public String getRefCode() {
return refCode;
}
public int getAge() {
return age;
}
public boolean isSubscribed() {
return subscribed;
}
public Immutable(String a, int b, boolean c) {
this.refCode = a;
this.age = b;
this.subscribed = c;
}
}
abstract class StrictImmutableBuilder {
public abstract String refCode();
public abstract int age();
public abstract boolean subscribed();
public Immutable build() {
return new Immutable(refCode(), age(), subscribed());
}
}
abstract class LaxImmutableBuilder {
private String refCode;
private int age;
private boolean subscribed;
protected void refCode(String refCode) {
this.refCode = refCode;
}
protected void age(int age) {
this.age = age;
}
protected void subscribed(boolean subscribed) {
this.subscribed = subscribed;
}
public Immutable build() {
return new Immutable(refCode, age, subscribed);
}
}
I'm experimenting with ways of creating immutable objects. The following builder objects
are quite attractive because they keep the role of the arguments clear. However I would like
to use the compiler to verify that certain fields are set, like with the Immutable()
constructor invocation. StrictImmutableBuilder
provides those checks, but is rather noisy. Is there some way to get the same checks but with the form of LaxImmutableBuilder
? Perhaps using annotations?
public class Immutable {
public static void main(String[] args) {
new Immutable("13272873C", 23, false);
// nice but what where those arguments?
new LaxImmutableBuilder() {{
refCode("13272873C");
age(23);
subscribed(false);
}}.build();
// now I know what each value represents
// but what if I forgot to set one?
new StrictImmutableBuilder() {
public String refCode() { return "13272873C"; }
public int age() { return 23; }
public boolean subscribed() { return false; }
}.build();
// now I'm forced to set each field, but now
// we have the extra noise of "return"
// and also "public" if we want to use
// this outside the current package
// is there another way? maybe using annotations?
}
private final String refCode;
private final int age;
private final boolean subscribed;
public String getRefCode() {
return refCode;
}
public int getAge() {
return age;
}
public boolean isSubscribed() {
return subscribed;
}
public Immutable(String a, int b, boolean c) {
this.refCode = a;
this.age = b;
this.subscribed = c;
}
}
abstract class StrictImmutableBuilder {
public abstract String refCode();
public abstract int age();
public abstract boolean subscribed();
public Immutable build() {
return new Immutable(refCode(), age(), subscribed());
}
}
abstract class LaxImmutableBuilder {
private String refCode;
private int age;
private boolean subscribed;
protected void refCode(String refCode) {
this.refCode = refCode;
}
protected void age(int age) {
this.age = age;
}
protected void subscribed(boolean subscribed) {
this.subscribed = subscribed;
}
public Immutable build() {
return new Immutable(refCode, age, subscribed);
}
}
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评论(2)
这是我使用的模式:
Here's the pattern I use:
有这个技巧:类型安全构建器模式
http://michid.wordpress.com/2008/08/13/type-safe-builder-pattern-in-java/
但这太疯狂了。
there is this trick: Type-safe Builder Pattern
http://michid.wordpress.com/2008/08/13/type-safe-builder-pattern-in-java/
but that's just too crazy.