[Java] Introduction to Java Programming 笔记 Chapter 10. 面向对象

对于字符串 string, 因为广泛使用，JVM为了提高效率，节省内存，如果两个字符串字面值相同，这两个string变量共享唯一一个实例， 这样的实例叫做限定字符串(interned string)

String s1 = "Welcome to Java";  // 限定字符串
String s2 = new String("Welcome to Java");
String s3 = "Welcome to Java";  // 同 s1，限定字符串

System.out.println("s1 == s2 is " + (s1 == s2));
System.out.println("s1 == s3 is " + (s1 == s3));

System.out.println("s1.equals(s2) is " + s1.equals(s2));
System.out.println("s1.equals(s3) is " + s1.equals(s3));

输出：

s1 == s2 is false
s1 == s3 is true
s1.equals(s2) is true
s1.equals(s3) is true

字符串的替换和分割：

"Welcome".replace('e', 'A') returns a new string, WAlcomA.
"Welcome".replaceFirst("e", "AB") returns a new string, WABlcome.
"Welcome".replace("e", "AB") returns a new string, WABlcomAB.
"Welcome".replace("el", "AB") returns a new string, WABcome.

String[] tokens = "Java#HTML#Perl".split("#");
for (int i = 0; i < tokens.length; i++)
    System.out.print(tokens[i] + " ");

显示：Java HTML Perl

重载的构造函数，参数少的可以调用参数多的，使用this关键字：

public BMI(String name, int age, double weight, double height) {
    this.name = name;
    this.age = age;
    this.weight = weight;
    this.height = height;
}

public BMI(String name, double weight, double height) {
    this(name, 20, weight, height); // 调用上一个构造函数
}

和数据域相关的方法： getter (or accessor)， setter (or mutator)

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