Java，将null分配给对象和仅声明有什么区别 [英] Java, What is the difference between assigning null to object and just declaration

问题描述

有什么区别:

• 对象 o = null;和
• Object o;(只是声明)

• Object o = null; and
• Object o; (just declaration)

谁能回答我?

推荐答案

这取决于你声明变量的作用域.例如，局部变量没有默认值，在这种情况下，您必须手动分配null，而>instance variables 分配 null 是多余的，因为实例变量获得默认值.

It depends on the scope where you declare the variable. For instance, local variables don't have default values in which case you will have to assign null manually, where as in case of instance variables assigning null is redundant since instance variables get default values.

public class Test {
    Object propertyObj1;
    Object propertyObj2 = null; // assigning null is redundant here as instance vars get default values 

    public void method() {
        Object localVariableObj1;
        localVariableObj1.getClass(); // illegal, a compiler error comes up as local vars don't get default values

        Object localVariableObj2 = null;
        localVariableObj2.getClass(); // no compiler error as localVariableObj2 has been set to null

        propertyObj1.getClass(); // no compiler error
        propertyObj2.getClass(); // no compiler error
    }
}

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