JAVA编程思想第五章练习题

 

练习1：

package JAVA5;

public class E01 {
    String s;

    public static void main(String[] args) {
        E01 s1 = new E01();
        System.out.println(s1.s);
    }
}

练习2：

package JAVA5;

public class E01 {
    String s1 = "a";
    String s2;
    E01(String s2i){
        s2 = s2i;
    }
    E01(){
        System.out.println("b");
    }
    public static void main(String[] args) {
        E01 s = new E01("ni");
        E01 s4 = new E01();
        System.out.println(s.s1);
        System.out.println(s.s2);
    }
}

练习3：

package JAVA5;

public class E03 {
    E03(){
        System.out.println("打印一条消息");
    }

    public static void main(String[] args) {
        E03 s = new E03();
    }
}

练习4：

package JAVA5;

public class E03 {
    E03(){
        System.out.println("打印一条消息");
    }
    E03(String s){
        String s2 = s;
        System.out.println(s2);
    }

    public static void main(String[] args) {
        E03 s = new E03();
        E03 s1 = new E03("你好");
    }
}

练习5：

package JAVA5;

class Dog{
    public void bark(int barking){
        System.out.println("Barking");
    }
    public void bark(double big){
        System.out.println("Big");
    }
}


public class E05Dog {

    public static void main(String[] args) {
        Dog dog = new Dog();
        dog.bark(1);
        dog.bark(1.0);
    }
}

练习6：

package JAVA5;

class Dog{
    public void bark(int barking,double big){
        System.out.println("Barking");
    }
    public void bark(double big,int barking){
        System.out.println("Big");
    }
}


public class E05Dog {

    public static void main(String[] args) {
        Dog dog = new Dog();
        dog.bark(1,1.0);
        dog.bark(1.0,1);
    }
}

练习7：

package JAVA5;
class Dog2{}
public class E07 {
    public static void main(String[] args) {
        Dog2 dog = new Dog2();
    }
}

练习8：

package JAVA5;

public class E08 {
    void bigdog(){
        bigbigdog();
        this.bigbigdog();
    }
    void  bigbigdog(){
        System.out.println("bigbigdog() called");
    }

    public static void main(String[] args) {
        new E08().bigdog();
    }
}

 

练习9：

package JAVA5;

public class E09 {
    public E09(int i){
        this("i = " + i);
    }
    public E09(String s){
        System.out.println("s = " + s);
    }


    public static void main(String[] args) {
        new E09("String call");
        new E09(47);
    }
}

练习10：

package JAVA5;

public class E10 {
    protected void finalize(){
        System.out.println("called");

    }
    public static void main(String[] args) {
        new E10();
    }
}

练习11：

package JAVA5;

public class E10 {
    protected void finalize(){
        System.out.println("called");

    }
    public static void main(String[] args) {
        new E10();
        System.gc();
        System.runFinalization();
    }
}

练习12：

package JAVA5;

class Tank{
    static int counter;
    int id = counter++;
    boolean full;
    public Tank(){
        System.out.println("Tank " + id + " created");
        full = true;
    }
    public void empty(){full = false;}
    protected void finalize(){
        if (full)
            System.out.println("Error: tank " + id + " must be empty at cleanup");
        else
            System.out.println("Tank " + id + " cleaned up OK");
    }
    public String toString(){return "Tank " + id;}
}
public class E12 {
    public static void main(String[] args) {
        new Tank().empty();
        new Tank();
        System.gc();
        System.runFinalization();
    }
}

 练习13： 

package JAVA5;

public class E13 {
    public static void main(String[] args) {
        System.out.println("Exercise left to reader");
    }
}

练习14：

package JAVA5;

public class E14 {
    static String s1 = "Initialized at definition";
    static String s2;
    static {s2 = "Initialized in static block";}

    public static void main(String[] args) {
        System.out.println("s1 = " + s1);
        System.out.println("s2 = " + s2);
    }
}

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练习15：

package JAVA5;

public class E15 {
    String s;
    { s = "'instance initialization'";}
    public E15(){
        System.out.println("Default constructor ; s = " + s);
    }
    public E15(int i ){
        System.out.println("int constructor; s = " + s);
    }

    public static void main(String[] args) {
        new E15();
        new E15(1);
    }
}

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练习16：

package JAVA5;

public class E16 {
    public static void main(String[] args) {
        String sa1[] = new String[4];
        sa1[0] = "ni";
        sa1[1] = "hao";
        sa1[2] = "ya";
        for(int i = 0; i < sa1.length; i++)
            System.out.println(sa1[i]);

        String sa2[] = {"ni","hao","ya"};
        for(int i = 0; i < sa2.length; i++)
            System.out.println(sa2[i]);
    }
}

练习17：

package JAVA5;
class Test{
    Test(String s){
        System.out.println("1 s = " + s);
    }
}
public class E17 {
    Test[] array1 = new Test[5];

    public static void main(String[] args) {
        Test[] array2 = new Test[5];
    }

}

练习18：

package JAVA5;

public class E18 {
    public static void main(String[] args) {
        Test[] array = new Test[5];
        for(int i = 0; i <array.length; i++)
            array[i] = new Test(Integer.toString(i));
    }
}

​​​​​​​ 

练习19：

package JAVA5;

public class E19 {
    static void printStrings(String... strs){
        for(String s:strs)
            System.out.println(s);
    }

    public static void main(String[] args) {
        printStrings("these" ,"are","some","strings");
        printStrings(new String[]{"these","are","some","strings"});
    }
}

练习20：

package JAVA5;

public class E20 {
    public static void main(String... args) {
        E19.printStrings(args);
    }
}

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练习21：

package JAVA5;
enum Paper{
    ONE,TWO,FIVE,TEN,TWENTY,FIFTY
}
public class E21 {
    public static void main(String[] args) {
        for(Paper s:Paper.values()){
            System.out.println(s + ".ordinal " + s.ordinal());
        }
    }

}

练习22：

package JAVA5;

public class E22 {
    static void describe(Paper pct){
        System.out.println(pct + " has a portrait of ");
        switch (pct){
            case ONE:
                System.out.println("1");
                break;
            case TWO:
                System.out.println("2");
                break;
            case TEN:
                System.out.println("10");
                break;
            case FIVE:
                System.out.println("5");
                break;
            case FIFTY:
                System.out.println("50");
                break;
            case TWENTY:
                System.out.println("20");
                break;
        }

    }

    public static void main(String[] args) {
        for(Paper s: Paper.values())
            describe(s);
    }
}