Guava – California Sunshine

Google Guava之Immutable Collection

Guava提供了很多Immutable Collection, 包括Set，Map，List等，使用起来简单方便，看看下面的例子。

import java.util.HashMap;
import java.util.Map;
 
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.ImmutableSortedMap;
import com.google.common.collect.ImmutableSortedSet;
 
 
public class TryImmutableMap {
 
    public static void main(String[] args) {
 
        Map<String, String> map = new HashMap<String, String>();
        map.put("abc", "def");
        map.put("def", "efg");
 
        // a immutable map is cloned from a regular map.
        ImmutableMap<String, String> aImmutalbeMap = ImmutableSortedMap.<String, String>copyOf(map);
 
        //aImmutalbeMap.put("tgh", "ihg"); // Exception!! You can't change it.
        //aImmutalbeMap.clear();            // Exception!! You can't change it.
        //aImmutalbeMap.remove("abc");        // Exception!! You can't change it.
 
        System.out.println(aImmutalbeMap.containsKey("abc")); // this line is ok.
 
        // for immutable set
        ImmutableSet<String> immutableSet = ImmutableSortedSet.<String>of("abc", "def", "efg");
        System.out.println(immutableSet); // output: [abc, def, efg]
 
        // for small immutable map
        ImmutableMap<String, String> immutableMap = ImmutableSortedMap.<String, String>of("abc", "def");
        System.out.println(immutableMap); // output: {abc=def}
 
    }
 
}

import java.util.HashMap;

import java.util.Map;

import com.google.common.collect.ImmutableMap;

import com.google.common.collect.ImmutableSet;

import com.google.common.collect.ImmutableSortedMap;

import com.google.common.collect.ImmutableSortedSet;

public class TryImmutableMap {

public static void main(String[] args) {

Map<String, String> map = new HashMap<String, String>();

map.put("abc", "def");

map.put("def", "efg");

// a immutable map is cloned from a regular map.

ImmutableMap<String, String> aImmutalbeMap = ImmutableSortedMap.<String, String>copyOf(map);

//aImmutalbeMap.put("tgh", "ihg"); // Exception!! You can't change it.

//aImmutalbeMap.clear(); // Exception!! You can't change it.

//aImmutalbeMap.remove("abc"); // Exception!! You can't change it.

System.out.println(aImmutalbeMap.containsKey("abc")); // this line is ok.

// for immutable set

ImmutableSet<String> immutableSet = ImmutableSortedSet.<String>of("abc", "def", "efg");

System.out.println(immutableSet); // output: [abc, def, efg]

// for small immutable map

ImmutableMap<String, String> immutableMap = ImmutableSortedMap.<String, String>of("abc", "def");

System.out.println(immutableMap); // output: {abc=def}

}

Google Guava之BiMap

今天介绍一个BiMap的小例子。

import com.google.common.collect.BiMap;
import com.google.common.collect.HashBiMap;
 
 
public class TryBiMap {
 
    public static void main(String[] args) {
        BiMap<String, String> aBiMap = HashBiMap.<String, String>create();
 
        aBiMap.put("abc", "def");
        aBiMap.put("defe", "abcd");
 
        System.out.println(aBiMap); // output: {abc=def, defe=abcd}
        System.out.println(aBiMap.get("abc")); // output: def
 
        // this line will throw a runtime exception
        // because there is "defe":"abcd" already. This record impacts BiMap.inverse.
        // aBiMap.put("abc", "abcd");
 
        // But we can use BiMap.forcePut to put the record of "abc":"abcd"
        // And the record "defe":"abcd" will be erased.
        aBiMap.forcePut("abc", "abcd");
 
        // Use BiMap.inverse() to get a inversed bimap.
        aBiMap = aBiMap.inverse();
 
        System.out.println(aBiMap); // output: {abcd=abc}
        System.out.println(aBiMap.get("abcd")); // output: abc
    }
}

import com.google.common.collect.BiMap;

import com.google.common.collect.HashBiMap;

public class TryBiMap {

public static void main(String[] args) {

BiMap<String, String> aBiMap = HashBiMap.<String, String>create();

aBiMap.put("abc", "def");

aBiMap.put("defe", "abcd");

System.out.println(aBiMap); // output: {abc=def, defe=abcd}

System.out.println(aBiMap.get("abc")); // output: def

// this line will throw a runtime exception

// because there is "defe":"abcd" already. This record impacts BiMap.inverse.

// aBiMap.put("abc", "abcd");

// But we can use BiMap.forcePut to put the record of "abc":"abcd"

// And the record "defe":"abcd" will be erased.

aBiMap.forcePut("abc", "abcd");

// Use BiMap.inverse() to get a inversed bimap.

aBiMap = aBiMap.inverse();

System.out.println(aBiMap); // output: {abcd=abc}

System.out.println(aBiMap.get("abcd")); // output: abc

}

Google Guava之Ordering

Guava提供的Ordering比Comparator强大很多，使用起来非常灵活。下面是个小例子。

import java.util.Arrays;
import java.util.Collections;
import java.util.List;
 
import com.google.common.base.Function;
import com.google.common.collect.Ordering;
 
 
public class TryOrdering {
 
    public static class A implements Comparable<A> {
        int a = 1;
        int b = 2;
 
        public A(int a, int b) {
            this.a = a;
            this.b = b;
        }
 
        public int getA() {
            return this.a;
        }
 
        public int getB() {
            return this.b;
        }
 
        @Override
        public String toString() {
            return String.format("{a=%d,b=%d}", this.a, this.b);
        }
 
        @Override
        public int compareTo(A o) {
            if (this.a > o.a) {
                return 1;
            } else if (this.a < o.b) {
                return -1;
            } else {
                if (this.b > o.b) {
                    return 1;
                } else if (this.b < o.b) {
                    return -1;
                } else {
                    return 0;
                }
            }
        }
    }
 
    enum AFunctions implements Function<A, Integer> {
        GET_A {
 
            @Override
            public Integer apply(A arg0) {
                return arg0.getA();
            }
 
        },
 
        GET_B {
 
            @Override
            public Integer apply(A arg0) {
                return arg0.getB();
            }
 
        }
    }
 
    public static void main(String[] args) {
        Ordering<A> aOrder =
            Ordering.natural()
                .nullsFirst()
                .onResultOf(AFunctions.GET_A)
                .compound(
                        Ordering
                            .natural()
                            .nullsFirst()
                            .onResultOf(AFunctions.GET_B))
                .nullsFirst()
                .reverse();
 
        List<A> as = Arrays.asList(
                        new A(1,2),
                        null,
                        new A(1,3),
                        new A(2,1),
                        new A(2,3),
                        null);
 
        System.out.println(aOrder.isOrdered(as)); // false
 
        Collections.sort(as, aOrder);
        System.out.println(as); // [{a=2,b=3}, {a=2,b=1}, {a=1,b=3}, {a=1,b=2}, null, null]
 
        System.out.println(aOrder.isOrdered(as)); // true
 
        A minA = Collections.min(as, aOrder);
        System.out.println(minA); // {a=2,b=3}
 
        A maxA = Collections.max(as, aOrder);
        System.out.println(maxA); // null
 
        List<A> subAList = aOrder.leastOf(as, 3);
        System.out.println(subAList); // [{a=2,b=3}, {a=2,b=1}, {a=1,b=3}]
    }
 
}

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import java.util.Arrays;

import java.util.Collections;

import java.util.List;

import com.google.common.base.Function;

import com.google.common.collect.Ordering;

public class TryOrdering {

public static class A implements Comparable<A> {

int a = 1;

int b = 2;

public A(int a, int b) {

this.a = a;

this.b = b;

}

public int getA() {

return this.a;

}

public int getB() {

return this.b;

}

@Override

public String toString() {

return String.format("{a=%d,b=%d}", this.a, this.b);

}

@Override

public int compareTo(A o) {

if (this.a > o.a) {

return 1;

} else if (this.a < o.b) {

return -1;

} else {

if (this.b > o.b) {

return 1;

} else if (this.b < o.b) {

return -1;

} else {

return 0;

}

enum AFunctions implements Function<A, Integer> {

GET_A {

@Override

public Integer apply(A arg0) {

return arg0.getA();

}

GET_B {

@Override

public Integer apply(A arg0) {

return arg0.getB();

}

public static void main(String[] args) {

Ordering<A> aOrder =

Ordering.natural()

.nullsFirst()

.onResultOf(AFunctions.GET_A)

.compound(

Ordering

.natural()

.nullsFirst()

.onResultOf(AFunctions.GET_B))

.nullsFirst()

.reverse();

List<A> as = Arrays.asList(

new A(1,2),

null,

new A(1,3),

new A(2,1),

new A(2,3),

null);

System.out.println(aOrder.isOrdered(as)); // false

Collections.sort(as, aOrder);

System.out.println(as); // [{a=2,b=3}, {a=2,b=1}, {a=1,b=3}, {a=1,b=2}, null, null]

System.out.println(aOrder.isOrdered(as)); // true

A minA = Collections.min(as, aOrder);

System.out.println(minA); // {a=2,b=3}

A maxA = Collections.max(as, aOrder);

System.out.println(maxA); // null

List<A> subAList = aOrder.leastOf(as, 3);

System.out.println(subAList); // [{a=2,b=3}, {a=2,b=1}, {a=1,b=3}]

}

Google Guava之Table

这个小例子介绍如何使用Guava提供的Table类。

import com.google.common.collect.HashBasedTable;
import com.google.common.collect.Table;
 
 
public class TryTable {
 
    public static void main(String[] args) {
 
        Table<String, String, String> aTable = HashBasedTable.create();
 
        // create a table;
        for (char a = 'A'; a <= 'C'; ++a) {
            for (char b = '1'; b <= '3'; ++b) {
                // put()
                // first is rowKey, second is columnKey, third is the value.
                aTable.put(Character.toString(a), Character.toString(b), String.format("%c%c", a, b));
            }
        }
 
        // query a specific column
        System.out.println(aTable.column("2")); // {A=A2, B=B2, C=C2}
 
        // query a specific row
        System.out.println(aTable.row("B")); // {3=B3, 2=B2, 1=B1}
 
        // query a cell
        System.out.println(aTable.get("B", "2")); // B2
 
        // contains test
        System.out.println(aTable.contains("D", "1")); // false
        System.out.println(aTable.containsColumn("3")); // true
        System.out.println(aTable.containsRow("C"));  // true
 
        System.out.println(aTable.columnMap()); // {3={A=A3, B=B3, C=C3}, 2={A=A2, B=B2, C=C2}, 1={A=A1, B=B1, C=C1}}
        System.out.println(aTable.rowMap()); // {A={3=A3, 2=A2, 1=A1}, B={3=B3, 2=B2, 1=B1}, C={3=C3, 2=C2, 1=C1}}
 
        // Remove a cell
        System.out.println(aTable.remove("B", "3")); // B3
    }
 
}

import com.google.common.collect.HashBasedTable;

import com.google.common.collect.Table;

public class TryTable {

public static void main(String[] args) {

Table<String, String, String> aTable = HashBasedTable.create();

// create a table;

for (char a = 'A'; a <= 'C'; ++a) {

for (char b = '1'; b <= '3'; ++b) {

// put()

// first is rowKey, second is columnKey, third is the value.

aTable.put(Character.toString(a), Character.toString(b), String.format("%c%c", a, b));

}

// query a specific column

System.out.println(aTable.column("2")); // {A=A2, B=B2, C=C2}

// query a specific row

System.out.println(aTable.row("B")); // {3=B3, 2=B2, 1=B1}

// query a cell

System.out.println(aTable.get("B", "2")); // B2

// contains test

System.out.println(aTable.contains("D", "1")); // false

System.out.println(aTable.containsColumn("3")); // true

System.out.println(aTable.containsRow("C")); // true

System.out.println(aTable.columnMap()); // {3={A=A3, B=B3, C=C3}, 2={A=A2, B=B2, C=C2}, 1={A=A1, B=B1, C=C1}}

System.out.println(aTable.rowMap()); // {A={3=A3, 2=A2, 1=A1}, B={3=B3, 2=B2, 1=B1}, C={3=C3, 2=C2, 1=C1}}

// Remove a cell

System.out.println(aTable.remove("B", "3")); // B3

}

Google Guava之Objects

Guava Objects是个非常好用的类，帮助我们写出hashCode(), equals()和toString()。

看下面的小例子。

public class TryObjects {
 
    private int i;
    private Double d;
 
    /**
     * Default ctor.
     */
    public TryObjects() {
        this(10, 1.0);
    }
 
    /**
     * Ctor with i and d.
     * @param i i
     * @param d d
     */
    public TryObjects(int i, double d) {
        this(i, d);
    }
 
    @Override
    public boolean equals(Object arg0) {
        if (arg0 == null || !(arg0 instanceof TryObjects)) {
            return false;
        } else {
            TryObjects obj = (TryObjects)arg0;
            return Objects.equal(this.i, obj.i)
                && Objects.equal(this.d, obj.d); // 不用担心null的情况
        }
    }
 
    @Override
    public int hashCode() {
        return Objects.hashCode(this.i, this.d);
    }

    @Override
    public String toString() {
        // TryObjects{i=10, d=1.0}
        return Objects.toStringHelper(TryObjects.class)
                .add("i", this.i)
                .add("d", this.d)
                .toString();
    }
}

public class TryObjects {

private int i;

private Double d;

/**

* Default ctor.

public TryObjects() {

this(10, 1.0);

}

/**

* Ctor with i and d.

* @param i i

* @param d d

public TryObjects(int i, double d) {

this(i, d);

}

@Override

public boolean equals(Object arg0) {

if (arg0 == null || !(arg0 instanceof TryObjects)) {

return false;

} else {

TryObjects obj = (TryObjects)arg0;

return Objects.equal(this.i, obj.i)

&& Objects.equal(this.d, obj.d); // 不用担心null的情况

}

@Override

public int hashCode() {

return Objects.hashCode(this.i, this.d);

}

@Override

public String toString() {

// TryObjects{i=10, d=1.0}

return Objects.toStringHelper(TryObjects.class)

.add("i", this.i)

.add("d", this.d)

.toString();

}