Thing in java 第5章，初始化和清理，练习题答案

Posted 2020-12-27 Me-Newbie

/**
 * Created by Sandy.Liu on 2018/7/28.
 * Thinking in java version 4, chapter 5, practice 2
 * Create a class which includes two string values, one is initialized at the point of defination,
 * another is initialized by constructor. What is the different between the two approach.
 */
public class Chap5Prac2 {
    Chap5Prac2(){
        s3 = "good bye";
    }
    String s1;
    String s2 = "hello";
    String s3;
    public static void main(String[] args){
        Chap5Prac2 t = new Chap5Prac2();
        P.print("t.s1: "+t.s1);
        P.print("t.s2: "+t.s2);
        P.print("t.s3: "+t.s3);
    }

}

/**
 * Created by Sandy.Liu on 2018/7/29.
 * Thinking in java version 4, chapter 5, practice 3
 * Create a constructor which prints message. Create a new object.
 */
public class Chap5Prac3DefaultConstructor{
    Chap5Prac3DefaultConstructor(){
        P.print("this is a default constructor");
    }
    public static void main(String[] args){

        Chap5Prac3DefaultConstructor dc = new Chap5Prac3DefaultConstructor();
    }
}

/**
 * Created by Sandy.Liu on 2018/7/29.
 * Thing in java version 4, chapter 5, practice 4
 * Add a overload constructor for the class in practice 3 that takes a string argument and prints it
 * along with your message.
 */
public class Chap5Prac4 {
    Chap5Prac4(){
        P.print("this is a default constructor");
    }
    Chap5Prac4(String s){
        P.print("This is an overload constructor with input parameter: "+s);
    }
    public static void main(String[] args){
        Chap5Prac4 t1 = new Chap5Prac4();
        Chap5Prac4 t2 = new Chap5Prac4("Hello");
    }
}

/**
 * Created by Sandy.Liu on 2018/7/29.
 * Thing in java version 4, chapter 5, practice 5
 * Create a class named Dog that has overload method bark(). This method will be overloaded by different
 * data type. Print all kind of barking() and howling() message. Write a main method to use all these
 * overload methods.
 */
public class Chap5Prc5Dog {
    void bark(){P.print("no parameter, quiet");}
    void bark(byte b){P.print("byte parameter: miao");}
    void bark(short s){P.print("short bark: wang");}
    void bark(int i){P.print("int bark: wangwang");}
    void bark(char c){P.print("char bark: chachacha");}
    void bark(float f){P.print("float bark: fafafa");}
    void bark(long l){P.print("long bark: lalala");}
    void bark(double d){P.print("double bark: doudoudou");}
    public static void main(String[] args){
        byte b = 1;
        short s = 2;
        char c = ‘c‘;
        Chap5Prc5Dog dog = new Chap5Prc5Dog();
        dog.bark();
        dog.bark(b);
        dog.bark(s);
        dog.bark(1);
        dog.bark(c);
        dog.bark(1L);
        dog.bark(1.0f);
        dog.bark(1.0);
    }
}

/**
 * Created by Sandy.Liu on 2018/7/29.
 * Thinking in java version 4, chapter 5, practice 6
 * Modify previous exercise, make two overloaded methods taking two parameters with different type but
 * reverse order, verify that works correctly.
 */
public class Chap5Prac6Dog1 {
    void bark(int i, String s){
        P.print("The first dog‘s name is " + s + ", it is "+i+" years old.");
    }
    void bark(String s, int i){
        P.print("The second dog‘s name is "+ s+", it is "+i+" years old.");
    }
    public static void main(String[] args){
        Chap5Prac6Dog1 dog = new Chap5Prac6Dog1();
        dog.bark(1, "dog1");
        dog.bark("dog2", 2);

    }
}

/**
 * Created by Sandy.Liu on 2018/7/29.
 * Thinking in java version 4, chapter 5, practice 7
 * Create a class which hasn‘t constructor, and then create a object of that class in main() to verify
 * if the default constructor is added automatically.
 */
public class Chap5Prac7Dog3 {
    void bark(){
        P.print("woof");
    }
    public static void main(String[] args){
        Chap5Prac7Dog3 dog = new Chap5Prac7Dog3();
        dog.bark();
    }
}

/**
 * Created by Sandy.Liu on 2018/7/29.
 * Thinking in java version 4, chapter 5, practice 8
 * Write a class which has two methods. Within the first method, call the second method twice:
 * this first time don‘t use this, and the second time use this.
 */
public class Chap5Prac8 {
    void method1(){
        method2();
        this.method2();
    }
    void method2(){
        P.print("this is method 2");
    }
    public static void main(String[] args){
        Chap5Prac8 test = new Chap5Prac8();
        test.method1();
    }
}

/**
 * Created by Sandy.Liu on 2018/7/30.
 * Thinking in java version 4, chapter 5, practice 9
 * Write a class with two overload constructors, and then call the second constructor by this in the
 * first constructor.
 */
public class Chap5Prac9This {
    Chap5Prac9This(int i){
        P.print("This is the first constructor, the give number is: "+i);
    }
    Chap5Prac9This(String s){
        this(7);
        P.print("this is the second constructor, the string is: "+s);
    }
    public static void main(String[] args){
        Chap5Prac9This ch = new Chap5Prac9This("sandy");
    }
}

/**
 * Created by Sandy.Liu on 2018/7/30.
 *  Thinking in java version 4, chapter 5, practice 10
 *  Write a class with finalize method which types a message. Create a new object in main{} for this
 *  class, and explain the behavior of the program.
 */
public class Chap5Prac10Finalize {
    boolean logout = false;
    Chap5Prac10Finalize(boolean logout){
        logout = logout;
    }
    void checkOut(){
        logout = false;
    }
    protected void finalize(){
        if(logout)
            P.print("error, logout");
    }
    public static void main(String[] args){
        Chap5Prac10Finalize ch = new Chap5Prac10Finalize(true);
        ch.checkOut();
        new Chap5Prac10Finalize(true);
        System.gc();


    }
}