Extract Method
將這段代碼放進一個獨立函數中，并讓函數名稱解釋該函數的用途。
void printOwing(double amount) {
printBanner();
//print details
System.out.println("name:" + _name);
System.out.println("amount" + amount);
}
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void printOwing(double amount) {
printBanner();
printDetails(amount);
}
void printDetails(double amount) {
System.out.println("name:" + _name);
System.out.println("amount" + amount);
}