JAVA编程思想第十一章练习题

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import java.util.ArrayList;

class Gerbil{
    private final int gerbilNumber;
    Gerbil(int gerbilNumber){
        this.gerbilNumber = gerbilNumber;
    }

    @Override
    public String toString() {
        return "Gerbil "+ gerbilNumber ;
    }

    public void hop(){
        System.out.println(this + " is hopping!");
    }
}
public class E01 {
    public static void main(String[] args) {
        ArrayList<Gerbil> gerbils = new ArrayList<>();
        for (int i = 0; i < 10; i++) {
            gerbils.add(new Gerbil(i));
        }
        for (int i = 0; i < gerbils.size(); i++) {
            gerbils.get(i).hop();
        }
    }
}

import java.util.Collection;
import java.util.HashSet;

public class SimpleCollection {
    public static void main(String[] args) {
        Collection<Integer> c = new HashSet<>();
        for (int i = 0; i < 10; i++) {
            c.add(i);
        }
        for(Integer i : c )
            System.out.print(i + ",");
    }
}

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Random;

public class E05 {
    static Random rand = new Random(47);

    public static void main(String[] args) {
        List<Integer> ints = new ArrayList<>(Arrays.asList(1,2,3,4,5,6,7));
        System.out.println("1: " + ints);
        ints.add(8);
        System.out.println("2: " +ints);
        System.out.println("3: " +ints.contains(8));
        ints.remove(Integer.valueOf(8));
        Integer i = ints.get(2);
        System.out.println("4: " + i + " " + ints.indexOf(i));
        Integer j = Integer.valueOf(1);
        
    }
}

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

class IDClass{
    private static int counter;
    private int count = counter++;

    @Override
    public String toString() {
        return "IDClass "+ count ;
    }
}
public class E07 {
    public static void main(String[] args) {
        IDClass[] idc = new IDClass[10];
        for (int i = 0; i < idc.length; i++) {
            idc[i] = new IDClass();
        }
        List<IDClass> lst = new ArrayList<IDClass>(Arrays.asList(idc));
        System.out.println("lst = " + lst);
        List<IDClass> subSet = lst.subList(lst.size()/4,lst.size()/2);
        System.out.println("subSet = " + subSet);
        subSet.clear();
        System.out.println("lst = " + lst);
    }
}

练习8：

import java.util.*;

public class E08 {
    public static void main(String[] args) {
        ArrayList<Gerbil> gerbils = new ArrayList<Gerbil>();
        for (int i = 0; i < 10; i++) {
            gerbils.add(new Gerbil(i));
        }
        for (Iterator<Gerbil> it = gerbils.iterator() ;it.hasNext();it.next().hop());
    }
}

练习11：

import java.util.*;

public class E11 {
    public static void printToStrings(Iterator<?> it){
        while (it.hasNext())
            System.out.println(it.next().toString());
    }
    @SuppressWarnings("unchecked")
    public static void main(String[] args) {
        List<Collection<String>> ca = Arrays.<Collection<String>>asList(
                new ArrayList<String>(),
                new LinkedList<String>(),
                new HashSet<String>(),
                new TreeSet<String>()
        );
        for (Collection<String> c : ca)
            printToStrings(c.iterator());
    }
}

 练习17：

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

public class E17 {
    public static void main(String[] args) {
        Map<String,Gerbil> map = new HashMap<>();
        map.put("Fuzzy",new Gerbil(1));
        map.put("Spot",new Gerbil(2));
        map.put("Joe",new Gerbil(3));
        map.put("Ted",new Gerbil(4));
        map.put("Heather",new Gerbil(5));
        Iterator<Map.Entry<String,Gerbil>> it = map.entrySet().iterator();
        while(it.hasNext()){
            Map.Entry<String,Gerbil> entry = it.next();
            System.out.print(entry.getKey() + ": ");
            entry.getValue().hop();
        }
    }
}