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面试准备

Core Java 面试题与答案

Test your skills through the online practice test: Core Java Quiz Online Practice Test

问题 51. What is the difference between a break statement and a continue statement?

A break statement results in the termination of the statement to which it applies (switch, for, do, or while). A continue statement is used to end the current loop iteration and return control to the loop statement.

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问题 52. Name the eight primitive Java types.

The eight primitive types are byte, char, short, int, long, float, double, and boolean.

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问题 53. Describe what happens when an object is created in Java?

Several things happen in a particular order to ensure the object is constructed properly:
1. Memory is allocated from heap to hold all instance variables and implementation-specific data of the object and its superclasses. Implementation-specific data includes pointers to class and method data.
2. The instance variables of the objects are initialized to their default values.
3. The constructor for the most derived class is invoked. The first thing a constructor does is call the constructor for its uppercase. This process continues until the constructor for java.lang.Object is called, as java.lang.Object is the base class for all objects in java.
4. Before the body of the constructor is executed, all instance variable initializers and initialization blocks are executed. Then the body of the constructor is executed. Thus, the constructor for the base class completes first and constructor for the most derived class completes last.

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问题 54. In Java, you can create a String object as below : String str = "abc"; & String str = new String("abc"); Why cant a button object be created as : Button bt = "abc"? Why is it compulsory to create a button object as: Button bt = new Button("abc"); Why this is not compulsory in String's case?

Button bt1= "abc"; It is because "abc" is a literal string (something slightly different than a String object, by-the-way) and bt1 is a Button object. That simple. The only object in Java that can be assigned a literal String is java.lang.String. Important to not that you are NOT calling a java.lang.String constuctor when you type String s = "abc";
For example String x = "abc"; String y = "abc"; refer to the same object. While String x1 = new String("abc");
String x2 = new String("abc"); refer to two different objects.

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问题 55. Does Java have "goto"?

No.

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