Effective Java Note-01 replaces constructors with static factory methods

Method in Java to get an object instance

1. Public constructor

Boolean bool = new Boolean("ture");
public Boolean(boolean value) {
    this.value = value;
}
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2. Static factory method

Boolean bool = Boolean.valueOf("ture");
public static Boolean valueOf(String s) {
    return parseBoolean(s) ? TRUE : FALSE;
}
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Advantages of the static factory approach

1. Static factory methods can have their own names.
2. Static factory methods can return the same object for repeated calls without creating a new instance for each call;

// TRUE and FALSE are static immutable properties of Boolean classes
public static final Boolean TRUE = new Boolean(true);
public static final Boolean FALSE = new Boolean(false);
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3. Static factory methods can return objects of any subtype of the original return type;
4. .

Disadvantages of the static factory approach

Static factory methods are hard to spot by programmers, so here are some common names:

1. From-type conversion method

Date date = Date.from(instant);
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2. Of – aggregation method

Set<Rank> faceCards = EnumSet.of(JACK, QUEUE, KING);
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3. The ValueOf – common

String str1 = String.valueOf(123);
Integer int1 = Integer.valueOf("123");
Long long1 = Long.valueOf("123");
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4. Instance or getInstance – The returned instance is described by the method’s arguments
5. Create or newInstance – returns a newInstance per call
6. .

Conclusion: Static factory approach is more suitable, remember the first reaction is to provide public constructor, not static factory!