Use static initialization block to initialize List / Set of static fields in Java

If you read the source code of SpringAOP, [this kind of code](http://grepcode.com/file/repo1.maven.org/maven2/org.springframework/spring-aop/4.2.0.RELEASE/org/springframework/ There was aop / aspectj / AspectJExpressionPointcut.java # AspectJExpressionPointcut) (code adjusted to remove noise).

`AspectJExpressionPointcut.java`


public class AspectJExpressionPointcut  {
    private static final Set<PointcutPrimitive> SUPPORTED_PRIMITIVES = new HashSet();

    static {
        SUPPORTED_PRIMITIVES.add(PointcutPrimitive.EXECUTION);
        SUPPORTED_PRIMITIVES.add(PointcutPrimitive.ARGS);
        SUPPORTED_PRIMITIVES.add(PointcutPrimitive.REFERENCE);
        SUPPORTED_PRIMITIVES.add(PointcutPrimitive.THIS);
        SUPPORTED_PRIMITIVES.add(PointcutPrimitive.TARGET);
        SUPPORTED_PRIMITIVES.add(PointcutPrimitive.WITHIN);
        SUPPORTED_PRIMITIVES.add(PointcutPrimitive.AT_ANNOTATION);
        SUPPORTED_PRIMITIVES.add(PointcutPrimitive.AT_WITHIN);
        SUPPORTED_PRIMITIVES.add(PointcutPrimitive.AT_ARGS);
        SUPPORTED_PRIMITIVES.add(PointcutPrimitive.AT_TARGET);
        logger = LogFactory.getLog(AspectJExpressionPointcut.class);
    }
}

This is a mechanism called Static Initialization Block. Until now, the initialization of List / Set etc. declared as static was written as ↓, but I feel that the static initialization block looks cleaner.

public class Hoge {
    private static final Set<PointcutPrimitive> SUPPORTED_PRIMITIVES = new HashSet(){{
        add(PointcutPrimitive.EXECUTION);
        add(PointcutPrimitive.ARGS);
        add(PointcutPrimitive.REFERENCE);
        add(PointcutPrimitive.THIS);
        add(PointcutPrimitive.TARGET);
        add(PointcutPrimitive.WITHIN);
        add(PointcutPrimitive.AT_ANNOTATION);
        add(PointcutPrimitive.AT_WITHIN);
        add(PointcutPrimitive.AT_ARGS);
        add(PointcutPrimitive.AT_TARGET);
    }};
}

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