ImmutableConverter.java

/*
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package org.jf.util;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.ImmutableSortedSet;

import javax.annotation.Nonnull;
import javax.annotation.Nullable;
import java.util.Comparator;
import java.util.Iterator;
import java.util.SortedSet;

public abstract class ImmutableConverter<ImmutableItem, Item> {
    protected abstract boolean isImmutable(@Nonnull Item item);
    @Nonnull protected abstract ImmutableItem makeImmutable(@Nonnull Item item);

    @Nonnull
    public ImmutableList<ImmutableItem> toList(@Nullable final Iterable<? extends Item> iterable) {
        if (iterable == null) {
            return ImmutableList.of();
        }

        boolean needsCopy = false;
        if (iterable instanceof ImmutableList) {
            for (Item element: iterable) {
                if (!isImmutable(element)) {
                    needsCopy = true;
                    break;
                }
            }
        } else {
            needsCopy = true;
        }

        if (!needsCopy) {
            return (ImmutableList<ImmutableItem>)iterable;
        }

        final Iterator<? extends Item> iter = iterable.iterator();

        return ImmutableList.copyOf(new Iterator<ImmutableItem>() {
            @Override public boolean hasNext() { return iter.hasNext(); }
            @Override public ImmutableItem next() { return makeImmutable(iter.next()); }
            @Override public void remove() { iter.remove(); }
        });
    }

    @Nonnull
    public ImmutableSet<ImmutableItem> toSet(@Nullable final Iterable<? extends Item> iterable) {
        if (iterable == null) {
            return ImmutableSet.of();
        }

        boolean needsCopy = false;
        if (iterable instanceof ImmutableSet) {
            for (Item element: iterable) {
                if (!isImmutable(element)) {
                    needsCopy = true;
                    break;
                }
            }
        } else {
            needsCopy = true;
        }

        if (!needsCopy) {
            return (ImmutableSet<ImmutableItem>)iterable;
        }

        final Iterator<? extends Item> iter = iterable.iterator();

        return ImmutableSet.copyOf(new Iterator<ImmutableItem>() {
            @Override public boolean hasNext() { return iter.hasNext(); }
            @Override public ImmutableItem next() { return makeImmutable(iter.next()); }
            @Override public void remove() { iter.remove(); }
        });
    }

    @Nonnull
    public ImmutableSortedSet<ImmutableItem> toSortedSet(@Nonnull Comparator<? super ImmutableItem> comparator,
                                                         @Nullable final Iterable<? extends Item> iterable) {
        if (iterable == null) {
            return ImmutableSortedSet.of();
        }

        boolean needsCopy = false;
        if (iterable instanceof ImmutableSortedSet &&
                ((ImmutableSortedSet)iterable).comparator().equals(comparator)) {
            for (Item element: iterable) {
                if (!isImmutable(element)) {
                    needsCopy = true;
                    break;
                }
            }
        } else {
            needsCopy = true;
        }

        if (!needsCopy) {
            return (ImmutableSortedSet<ImmutableItem>)iterable;
        }

        final Iterator<? extends Item> iter = iterable.iterator();


        return ImmutableSortedSet.copyOf(comparator, new Iterator<ImmutableItem>() {
            @Override public boolean hasNext() { return iter.hasNext(); }
            @Override public ImmutableItem next() { return makeImmutable(iter.next()); }
            @Override public void remove() { iter.remove(); }
        });
    }

    @Nonnull
    public SortedSet<ImmutableItem> toSortedSet(@Nonnull Comparator<? super ImmutableItem> comparator,
                                                @Nullable final SortedSet<? extends Item> sortedSet) {
        if (sortedSet == null || sortedSet.size() == 0) {
            return ImmutableSortedSet.of();
        }

        @SuppressWarnings("unchecked")
        ImmutableItem[] newItems = (ImmutableItem[])new Object[sortedSet.size()];
        int index = 0;
        for (Item item: sortedSet) {
            newItems[index++] = makeImmutable(item);
        }

        return ArraySortedSet.of(comparator, newItems);
    }
}