Java - Thinking in Java 第5章 習題

標籤：mystra   java   

1

//: Main.java/** * String初始化 */class Test {    String s;}class Main {    public static void main(String[] args) {        Test t = new Test();        System.out.println("s = " + t.s);    }}/** * Output: s = null *///:~

2

初始化效果相同, 成員變數定義初始化定義時確定, 構造初始化構造時確定.

//: Main.java/** * 初始化 */class Test {    String s1;    String s2 = "haha";    String s3;    Test () {        s3 = "hehe";    }}class Main {    public static void main(String[] args) {        Test t = new Test();        System.out.println("s1 = " + t.s1);        System.out.println("s2 = " + t.s2);        System.out.println("s3 = " + t.s3);    }}/** * Output: s1 = null s2 = haha s3 = hehe *///:~

3

//: Main.java/** * 預設構造器 */class Test {    Test () {        System.out.println("This is Test");    }}class Main {    public static void main(String[] args) {        Test t = new Test();    }}/** * Output: This is Test *///:~

4

//: Main.java/** * 預設構造器 */class Test {    Test () {        System.out.println("This is Test");    }    Test (String s) {        System.out.println("Test : " + s);    }}class Main {    public static void main(String[] args) {        Test t = new Test("Hello");    }}/** * Output: Test : Hello *///:~

5

//: Main.java/** * 構造器重載 */class Dog {    Dog() {        System.out.println("Wang! Wang! Wang!");    }    Dog(String s) {        System.out.println("Barking!");    }    Dog(int i) {        System.out.println("Howling!");    }}class Main {    public static void main(String[] args) {        Dog d1 = new Dog();        Dog d2 = new Dog("Hello");        Dog d3 = new Dog(1);    }}/** * Output: Wang! Wang! Wang! Barking! Howling! *///:~

6

//: Main.java/** * 構造器重載-參數順序不同 */class Dog {    Dog() {        System.out.println("Wang! Wang! Wang!");    }    Dog(String s, int i) {        System.out.println("Barking!");    }    Dog(int i, String s) {        System.out.println("Howling!");    }}class Main {    public static void main(String[] args) {        Dog d1 = new Dog();        Dog d2 = new Dog("Hello", 1);        Dog d3 = new Dog(1, "Hello");    }}/** * Output: Wang! Wang! Wang! Barking! Howling! *///:~

7

//: Main.java/** * 預設構造器 */class Test {    String s = "Hello World";}class Main {    public static void main(String[] args) {        Test t = new Test();        System.out.println(t.s);    }}/** * Output: Hello World *///:~

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Java - Thinking in Java 第5章 習題