Why is this the program's output?

public class OverloadingTest extends Format{ public int add(String s1){ System.out.println("With String"); return 1; } public int add(Object a){ System.out.println("With Object"); return 1; } public static void main(String[] args) { OverloadingTest overloadingTest = new OverloadingTest(); overloadingTest.add(null); } } Wh

为什么这是该程序的输出?

public class OverloadingTest extends Format{ public int add(String s1){ System.out.println("With String"); return 1; } public int add(Object a){ System.out.println("With Object"); return 1; } public static void main(String[] args) { OverloadingTest overloadingTest = new OverloadingTest(); overloadingTest.add(null); } }

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Credit Card validator for java

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