标签：gre air xpl als iso nal att through uri
You could have built an object with this:
// Example 1
new FlyingMachine("Boeing 787", 2, false);
Or this:
// Example 2
FlyingMachine plane = new FlyingMachine();
plane.setName("Boeing 787");
plane.setNumEngine("Boeing 787");
plane.setHasRocketBooster(false);
In example one, the object is created through constructor. There are multiple downsides with this
The arguments passing into the constructor are not meaningful
What the hell does 2 and false exactly mean?
In comparison the builder pattern has done a great job explaining the values .numEngine(2) and .hasRocketBooster(false)
The arguments are all passed in one line making it nearly impossible to read
You may arrange like this
new FlyingMachine( "Boeing 787", 2, false);
But I doubt it really improves readability
You cannot omit parameters
When one day you realize that you do not want to name that flying machine, you may choose to pass in null for name
new FlyingMachine(null, 2, false);
But using the builder pattern, you can simply remove this line: .name("Boeing 787")
In example two, the internal properties of the object are set by setters after instantiation. It essentially achieves the same effects as the two other methods, but it has a completely different semantic meanings. This method creates an empty object and fills in the details later, which bypasses the constructor completely and these properties cannot be used during initialization. In reality, you won’t build an aircraft without knowing what’s inside, right?
摘录自 effective java
public class DoDoContact {
private final int age;
private final int safeID;
private final String name;
private final String address;
public static class Builder {
private int age = 0;
private int safeID = 0;
private String name = null;
private String address = null;
// name必要
public Builder(String name) {
this.name = name;
}
public Builder age(int val) {
age = val;
return this;
}
public Builder safeID(int val) {
safeID = val;
return this;
}
public Builder address(String val) {
address = val;
return this;
}
public DoDoContact build() {
// 通过builder构建实例
return new DoDoContact(this);
}
}
private DoDoContact(Builder b) {
age = b.age;
safeID = b.safeID;
name = b.name;
address = b.address;
}
}
DoDoContact ddc = new DoDoContact.Builder("Ace").age(10)
.address("beijing").build();
System.out.println("name=" + ddc.getName() + "age =" + ddc.getAge()
+ "address" + ddc.getAddress());
reference：
https://www.cnblogs.com/moonz-wu/archive/2011/01/11/1932473.html
https://hermannyung.com/2017/05/28/builder-pattern-vs-constructor-vs-setter/
标签：gre air xpl als iso nal att through uri
原文地址：https://www.cnblogs.com/lnas01/p/10367002.html
